Digital Audio Essentials | O'Reilly Media

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In the simplest terms, computer audio is a catch-all concept for music or other audio that is created, listened to, downloaded, shared, or edited using a personal computer. By nature, all computer audio is digital audio, but unlike the digital audio on compact discs (CDs) and MiniDiscs, computer audio isn't tied to specific media.

The term downloadable music refers to music in the form of digital audio files (MP3 files are a good example) that you can download from a web site, play on your computer or portable player, or burn to a CD. Streaming audio uses similar technology but allows you to listen to music via an Internet connection, similar to the way you listen to AM and FM radio.

The concept of downloadable music evokes a world without records, tapes, or pre-recorded CDs, while streaming audio suggests a world without transmitters, antennas, or geographic limitations. Both technologies have spawned legal and philosophical discussions that rage across the Web and throughout the courts. Digital audio and downloadable music have, without a doubt, changed the face of the recording industry, the way we listen to music, and the way we'll consume music and other types of audio in the future.

Your personal computer is an amazingly capable device for recording and playing audio. You have some incredible capabilities at your fingertips, thanks to technologies that compress audio such as MP3 and Windows Media Audio (WMA); hard disks that can store thousands of songs; and the ability to download music from the Internet. Here are a few examples:

Your computer can function as a digital jukebox that stores thousands of songs, which you can organize into custom playlists and play with a click of the mouse (and the right audio software).
Formats such as MP3 and WMA let you copy your entire music collection to a portable player the size of a cigarette pack, which can store more than 10,000 songs at near CD quality.

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Your personal computer is an amazingly capable device for recording and playing audio. You have some incredible capabilities at your fingertips, thanks to technologies that compress audio such as MP3 and Windows Media Audio (WMA); hard disks that can store thousands of songs; and the ability to download music from the Internet. Here are a few examples:

Your computer can function as a digital jukebox that stores thousands of songs, which you can organize into custom playlists and play with a click of the mouse (and the right audio software).
Formats such as MP3 and WMA let you copy your entire music collection to a portable player the size of a cigarette pack, which can store more than 10,000 songs at near CD quality.
Using the Internet, you can sample and purchase a wide variety of music from the comfort of your home and find great music from independent artists you might not otherwise know about.
You can listen to thousands of Internet radio stations from all over the world. If you hear a song you like, you can often purchase it on the spot and download it to your computer.
With software for recording and editing audio, you can "digitize" your tapes and records; remove the hiss, clicks, and pops; and store the audio on a CD that will last for decades without losing any sound quality.
You can record more than 12 hours of digitally compressed music onto a single CD in a few minutes, rather than the dozen or more hours it would take to record the same music with a cassette recorder.
If you're an independent artist, you can promote your music worldwide and keep in touch with fans, or you can sign with an Internet record label, retain the copyrights to your music, and keep a larger share of the revenue.

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Digital music first became available to the masses in 1982, when Phillips introduced the CD. Six years later, sales of CDs surpassed those of vinyl records. However, downloadable music and streaming audio have now touched off a revolution that is rapidly and radically changing the way music is distributed and consumed. This revolution is already far more important than when compact discs displaced vinyl records in the early 1980s, because physical media is being replaced by electronic bits that don't require factories, packages, warehouses, or shipping.

In 1992, the Moving Picture Experts Group (MPEG) released the specification for MP3. By mid-1999, "MP3" had edged out "sex" as the most popular Internet search term—and within 4 years, more than 400 million copies of various file-sharing programs had been downloaded, and billions of songs had been shared without any compensation to copyright holders. Meanwhile, the Recording Industry Association of America (RIAA) reported that music CD sales, which reached a high of $13.2 billion in 2000, were down to $11.2 billion in 2003—with downloadable music (particularly illegal file sharing, which we'll cover later) at the heart of the losses.

The MPEG committee, which works under the direction of the International Standards Organization (ISO), establishes standards for encoding audio and video in digital format and for interactive graphics applications. MP3 is just a small part of the MPEG family of standards. Thanks to MPEG, we also have standards for technologies such as DVD (Digital Versatile Disc) and DirecTV.

Music plays an important role in our lives, affecting our moods and making us feel connected to the rest of the world. But finding music to suit our personal tastes requires a lot of time and effort. That's why we have record labels and radio stations: they act as filters for the music we hear and save us the trouble of sifting through thousands of new songs every year.

However, any student of human nature can easily predict the problem with such filters. Record labels and radio stations decide, for the most part, what we listen to and when. We consumers have little say in this process, other than our ability to vote with our wallets and the dials on our radios. That's not enough for many of us.

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Just about any PC or Mac produced since the year 2000 will be more than powerful enough to create and manage your digital music library. But if you have an older computer, how can you tell if it's good enough for digital audio?

The first section of this chapter covers the basic hardware and software requirements for digital audio applications, along with the pros and cons of upgrading individual components versus purchasing a new computer.

The remaining sections of this chapter cover key functions of the components that have the greatest effect on performance, including CPUs, memory, and hard disk drives. We also cover the details of common computer interfaces, CD and DVD drives, sound cards, and computer speakers.

If you are just interested in having a computer that does what you want and you don't want to learn the nitty-gritty of how and why, we have some good news: you can skip the technical details in the last half of this chapter.

Does your computer have what it takes to play, record, or edit digital audio? How good is good enough? The answers will be different for everyone. Simply put, you need enough power to process the audio without hesitation or skips, while running any other programs you need to use at the same time (such as an email client, web browser, or personal organizer).

Beyond the minimum requirements, the issue boils down to how much it costs to increase performance to a certain level. If a 40-MB audio file loads in 10 seconds, and it takes 40 seconds for your editing software to perform a common process on it (adjust the volume, for example), is it worth spending $2,000 on a new system to cut these times in half?

Today, you can find computers just a few aisles over from the big-screen TVs and microwave ovens at your local "big box" retailer. Computers are becoming just another household appliance, like toasters.

Just as any toaster will make toast, any computer sold today will play digital audio. As with computers, some toasters come in fancy brushed stainless steel cases and cost many times more than a basic model (although often, the insides are the same). Some will appeal to the gadget lovers, with a multitude of knobs and settings. You'd better know what you're doing with these types, or you'll end up making blackened lumps—and be warned, when they break, there's no simple fix, and you'll have to take them in for service.

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Does your computer have what it takes to play, record, or edit digital audio? How good is good enough? The answers will be different for everyone. Simply put, you need enough power to process the audio without hesitation or skips, while running any other programs you need to use at the same time (such as an email client, web browser, or personal organizer).

Beyond the minimum requirements, the issue boils down to how much it costs to increase performance to a certain level. If a 40-MB audio file loads in 10 seconds, and it takes 40 seconds for your editing software to perform a common process on it (adjust the volume, for example), is it worth spending $2,000 on a new system to cut these times in half?

Today, you can find computers just a few aisles over from the big-screen TVs and microwave ovens at your local "big box" retailer. Computers are becoming just another household appliance, like toasters.

Just as any toaster will make toast, any computer sold today will play digital audio. As with computers, some toasters come in fancy brushed stainless steel cases and cost many times more than a basic model (although often, the insides are the same). Some will appeal to the gadget lovers, with a multitude of knobs and settings. You'd better know what you're doing with these types, or you'll end up making blackened lumps—and be warned, when they break, there's no simple fix, and you'll have to take them in for service.

Each system will appeal to a different type of user, so think about which type of toaster you'd buy before choosing your computer. Check out the manufacturer or store's reputation before buying. PC Magazine (http://www.pcmag.com) regularly publishes articles about computer service and reliability, while CNET (http://www.cnet.com) reviews the latest models and tests their performance.

If you work with files like this only a few times each day, probably not. But if you routinely work with large files, or you work in a production environment, an expense of a few thousand dollars to cut processing times in half is easily justified. On the other hand, a $200 upgrade that gives you the same increase in performance would probably make sense for anyone.

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Following are the basic elements that make up any computer and, of course, affect its performance. We'll cover some of the elements in more detail later in the chapter.

Your computer's central processing unit (CPU) is like a car's engine. A V8 will let you go faster, but a six-cylinder engine will get you around just fine. The V8 makes more sense if you regularly pull a heavy trailer, though. The six-cylinder might be able to pull the trailer on level ground, but it will have trouble on steep hills. If you need to pull an even heavier trailer or need to get up those steep hills fast, the six-cylinder is no longer an option. All computers manufactured since around 2000 have the equivalents of V8 engines for processors.

On most computers, you can replace the processor with one of the same type, but with a higher clock speed. However, the performance gain is usually small. Upgrading to a different type of processor—say, from a Pentium III to a Pentium 4—rarely makes sense, because you have to replace the motherboard and memory at the same time, and the costs can easily approach those of buying a new computer.

If you have a recently manufactured computer, upgrading to a system with a more powerful processor makes sense only in the following scenarios:

You are a speed demon or gadget-hound and want your computer to go as fast as possible, regardless of the cost.
You play a lot of graphics- and processor-intensive computer games.
You are a power user or audio/video editor who works with large files and likes to multitask between several different programs.

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In this section, we'll describe the computer components that have the most effect on the performance of applications that work with digital audio. These details will help you understand how to squeeze the best performance out of your existing computer without spending a fortune.

A computer's central processing unit, or CPU, is its brain. All of the information handled by your computer is managed and directed by the CPU. The CPU loads programs and data from the hard drive and moves data between memory, graphics cards, sound cards, mice, and keyboards. The clock speed and processor architecture of the CPU determine how fast it can process information.

The processor architecture (or class) relates to the performance of a CPU, similar to the way the number of cylinders and type of fuel system (carburetor or fuel injection) relate to the performance of a car engine. The processor's clock speed is like the revolutions per minute (rpm) of a car engine. Increasing the clock speed of a processor within the same class will result in better performance, just as increasing the rpm of an engine will result in more horsepower. However, clock speed is meaningless in comparing the performance of processors from different classes; it would be like saying that a single-cylinder lawnmower engine operating at 3000 rpm should outperform a fuel-injected V8 engine running at 2000 rpm.

In addition to the CPU, many other components, such as the hard disk capacity and amount of RAM, affect the performance of your computer. Simply installing a faster processor won't make a computer run faster if the other components can't keep up—it would be like putting a V8 engine in a lawnmower.

If you've evaluated the potential benefits versus the cost and decided that a processor upgrade does make sense, consider the following tips.

The design of a computer's motherboard determines the type of processor it can use. For example, motherboards designed for Pentium III processors can't use Pentium, Pentium II, or Pentium 4 processors. Even a Pentium III motherboard can't take just any Pentium III processor, since there are over 20 variations of the Pentium III CPU. Because of all the variables, we don't recommend do-it-yourself processor upgrades for anyone but extremely technical users.

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Optical drives, which most of us know as CD or DVD drives, are standard in virtually all new personal computers. CD and DVD technologies are based on similar principles, although DVD is a newer technology that offers much higher capacity.

The CD drives used in personal computers come in several different types: CD-ROM, CD-R, and CD-RW. All CD-R and CD-RW drives can also function as CD-ROM drives, and virtually all CD-RW drives can also burn CD-R discs. We'll cover CD media and formats in depth in Chapter 15, but for now, here's a short overview of the basics.

CD-ROM: CD-ROM stands for Compact Disc-Read Only Memory. CD-ROM drives can read several types of data CDs (including, often, CD-RW discs) and play standard audio CDs. CD-ROM drives can also "rip" songs from audio CDs to your computer's hard drive (see Chapter 11).
CD-R: CD-R stands for CD-Recordable. Once you record something on a CD-R disc, you can't erase or edit the information. CD-Rs are good for making custom audio CDs, sending large files to other people, and making permanent backups of computer data.
CD-RW: CD-RW stands for CD-Rewritable. CD-RW discs can be erased and re-recorded hundreds of times. CD-RWs work well for short-term backups, but they are not good a choice for recording standard audio CDs, because CD-RWs won't work in many standard CD players.

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Modern computers use a number of general-purpose interfaces to communicate with external devices, such as hard drives, CD/DVD drives, printers, scanners, and digital cameras. Following are descriptions of some common interfaces, and Table 2-4 breaks them down at a glance. Serial (RS-232) and parallel (Centronics) interfaces are rapidly fading away and are being replaced by the faster and more flexible USB and FireWire.

Table 2-4: External intefaces
Interface	Maximum transfer rate	Commonly used for
Serial (RS232)	115 Kbps	External modems, mice
Parallel (ECP)	1 Mbps	Older printers and external drives
USB 1.0/1.1	11 Mbps	Digital cameras, external hard disks and CD/
USB 2.0	480 Mbps	DVD drives, printers and scanners, portable
		digital audio players, external audio devices
FireWire	400 Mbps	Digital video cameras, external hard disks and

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Everything else being equal, the quality of your sound card and speakers will have the greatest effect on the quality of any audio played through your computer.

A sound card performs many functions, including analog-to-digital (A/D) and digital-to-analog (D/A) conversion, audio mixing, music synthesizing, sound effects generation, and amplification.

During playback, the digital signal must be converted to an analog signal, to drive headphones or feed an amplifier for speakers. This happens in a device called a digital-to-analog converter.

The components inside a computer generate a tremendous amount of electrical noise. This noise can be introduced into the audio signal whenever it is in an analog format. Poor shielding allows noise to leak into the signal, and low-quality D/A converters add distortion and even more noise.

The most important features for a basic sound card are good shielding and good digital-to-analog converters. Digital connectors are important if you want to interface with a digital device, such as a MiniDisc player or a stereo receiver that has digital inputs and outputs.

The term shielding refers to metal that surrounds a circuit or a wire carrying a signal. The shield intercepts electrical noise before it can interfere with the signal and carries it away to ground. Ground refers literally to the ground beneath your feet. The metal case of your computer is connected to a ground wire. This connects to the center hole in the wall plug, which connects to a wire that leads to a metal stake, driven into the earth.

If you play computer games, look for a sound card that includes a game port (joystick) connector. Most game ports can also double as an interface to external MIDI devices. If you want to take advantage of games that support surround sound, you need a sound card with front and rear speaker outputs or a digital output that supports surround sound.

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If you've taken the time to put your music collection on your computer, you'll probably want to listen to it through a good sound system—or at least one that's better than your cheap computer speakers. Consider combining your computer's capabilities for organizing and playing music with the high fidelity of a home stereo or home theater system. You'll get the best of both worlds, without spending lots of money on amplified computer speakers that probably are no match for the power and fidelity of your existing stereo system.

You have a wide range of options when it comes to making the stereo connection. Basic solutions just get the audio from your sound card to your stereo. More advanced choices include wireless connections, remote controls, and displays that let you access your jukebox program from anywhere in your house. You don't need expensive wiring for these options, and you can quit running back and forth during parties to change playlists or see what's playing.

This chapter covers the many different ways of distributing and enjoying computer-based music throughout your house. We'll discuss the pros and cons of different types of connections, including analog and digital cabling, wireless audio transmitters, and wireless networks. You'll learn about the common types of audio connectors and cables, how to identify the right inputs and outputs, and how to match signal levels for the cleanest possible sound. We'll also show you how to connect a tape deck or a turntable to your computer so you can "digitize" your records and tapes (see Chapter 14) and manage them with your jukebox program, just as you do your downloaded MP3s.

Even with wireless audio transmitters, some cables are required, so we'll begin with a discussion of basic terminology and descriptions of common audio connectors and cables. Figure 3-1 shows several common types of connectors used for analog and digital audio. Some, such as XLR, are used primarily for professional audio equipment, while others, such as 1/8" mini-phone jacks, are used mostly for consumer equipment. Many connectors, including XLR, RCA, and 1/8" mini-phone jacks, are used for both digital and analog applications.

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Even with wireless audio transmitters, some cables are required, so we'll begin with a discussion of basic terminology and descriptions of common audio connectors and cables. Figure 3-1 shows several common types of connectors used for analog and digital audio. Some, such as XLR, are used primarily for professional audio equipment, while others, such as 1/8" mini-phone jacks, are used mostly for consumer equipment. Many connectors, including XLR, RCA, and 1/8" mini-phone jacks, are used for both digital and analog applications.

Figure 3-1: Audio connectors

Tables 3-1 and 3-2 show common applications for different types of connectors. Balanced connections (see Table 3-1) automatically cancel out interference and are found mainly on pro audio equipment. Digital connections (Table 3-2) can carry multiple channels through a single conductor, but separate jacks are still required for inputs and outputs. Note that some connectors, such as RCA and 1/8" mini-phone jacks, can be used for either analog or digital applications.

Table 3-1: Analog connectors
Connector	Conductors	Commonly used for
RCA (phono)	Two (mono)	Home audio interconnect (two required), sound card line-in/out
Stereo 1/8" mini-phone	Three (stereo)	Headphones, sound card line-in/out, portable player line-in/out

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When you play audio on your computer, a digital signal travels to the sound card. (Refer back to Chapter 2 for more on sound cards.) The signal is converted to analog and sent to the analog output jacks (typically a line-out and headphone-out), and on some sound cards it may also be passed along without modification to a digital output jack.

When you're recording, on the other hand, the audio signal is fed into one of the input jacks. If the signal is analog (e.g., feeds from microphones and any equipment with line-out jacks, such as tape decks and stereo receivers), it is converted to digital before it's passed on to the recording program on the computer. If the incoming signal is digital (e.g., from a MiniDisc player or stereo receiver with digital outputs), it can be passed along without conversion.

Basic sound cards, such as those that ship with most home computers and virtually all notebook computers, use 1/8" mini-phone jacks for all inputs and outputs. A mono jack serves as the microphone input, and stereo jacks are used for the line-in and line-out. Stereo jacks save space because they carry both channels through a single connector. Adapter cables are available to connect stereo 1/8" mini-phone jacks to the separate left and right RCA jacks found on most home stereos.

Higher-end sound cards may include separate RCA jacks for the left and right channels—the same layout found on most home stereo systems. High-end sound cards may also have jacks for digital inputs and outputs. These can be used to connect to digital inputs on your stereo receiver or to digital devices such as MiniDisc recorders or external digital-to-analog (D/A) converters. Many sound cards also include a special multi-pin "D" connector, which serves as an interface to a game controller (joystick) or to external MIDI devices, but this does not carry audio signals.

Figure 3-2 shows sound cards with several types of jacks. Most sound cards have 1/8" mini-phone connectors for the microphone, line-level input, and line-level output. Some higher-end sound cards (left) have separate right and left RCA connectors for the line-out. Table 3-3 shows the functions of common inputs and outputs found on most sound cards. The term "level" is used in Table 3-3 in a context that applies only to analog signals. See Chapter 8 for an explanation of the differences between analog and digital signals.

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Most home stereo equipment uses RCA jacks for analog inputs and outputs (see Figure 3-3). On a home stereo receiver, the tuner, CD, and tape-in (play) jacks are line-level inputs. The tape-out (record) and preamp-out (sometimes labeled aux-out) jacks are line-level outputs. The headphone jack has a stereo 1/8" mini-phone or 1/4" phone connector. Table 3-4 shows the functions of common inputs and outputs found on stereo receivers.

Figure 3-3: Typical stereo receiver input and output jacks

Table 3-4: Stereo receiver input and output jacks
Type	Input	output	Level	Jacks
Headphone			High	Stereo 1/4" phone or 1/8" mini-phone
Phono			Low	Two RCA

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A direct cable from your sound card to your stereo receiver is the least expensive and most straightforward approach to connecting the two. For most people this will be an analog connection, because the majority of consumer audio equipment and sound cards include analog inputs and outputs. Audiophiles with the right equipment may prefer the digital route.

A drawback of analog connections is that improperly shielded cables are prone to picking up noise, and running cable over a long distance (more than six feet) can result in some loss of high frequencies (treble). However, an analog connection with high-quality coaxial cables can transmit very high-fidelity sound.

The simplest method of playing music on your computer through your home stereo is to make an analog connection between the two. To do this, simply run a cable from the line-out jack of your sound card to a line-level input of your stereo receiver, as shown in Figure 3-4.

Figure 3-4: Analog connection to stereo

If your sound card's line output is a stereo 1/8" mini-phone jack, you'll need a splitter cable to separate the left and right signals into two RCA connectors. The end of the cable that plugs into the sound card will have a stereo 1/8" mini-phone plug, and the end that plugs into your stereo will have two RCA plugs.

Splitter cables can be found at most stores that sell home stereo systems. If you can't find a long enough splitter cable, you can use an adapter with a standard male-to-male RCA audio cable. An adapter may be either a solid one-piece type or a short length of cable. One end will have a stereo 1/8" mini-phone plug, and the other end will have two RCA jacks.

To record from a stereo system to your computer, you can use the same type of cable and adapter. Connect the end with the RCA plugs to a line-out (or record) jack on your receiver, and connect the other end to the line-in jack on your sound card.

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The quality of the cables you use can have a noticeable effect on the quality of the sound, whether you're making an analog or digital connection.

Most stores that sell home entertainment systems will carry decent-quality cables, but it's difficult to determine quality just by looking at a cable. Monster Cable (http://www.monstercable.com) offers a line of high-quality audio cables that can be purchased online and in most stores that sell stereo equipment. Radio Shack also carries high-quality audio cables.

Following are descriptions of the characteristics that affect the performance of audio cables.

Audio interconnect cables have an insulated wire in the center, surrounded by a braided metal or foil shield. Higher-quality interconnect cables have braided shields and are usually thicker than lower-quality cables. Speaker cables are normally unshielded and are not suitable for interconnecting audio equipment.

Beware of headphone extension cords with 1/8" mini-phone plugs and of speaker cables with RCA connectors. These cables are normally unshielded and will pick up a lot more noise than shielded cables.

The term low capacitance frequently appears in discussions about audio cables, as in "lower is better." You might be wondering, "What is capacitance anyway, and why should I care?" The short answer is that high-capacitance cables can cause loss of high frequencies (treble) with long cables (over six feet).

The long answer is that capacitance is an electrical characteristic that affects the load a cable places on a signal. The load is greater for higher frequencies and increases with the length of the cable. Higher capacitance results in a higher load, which reduces the high frequencies delivered to your stereo, thereby degrading the sound.

Many factors affect the capacitance of an audio cable, including its length, the material used for the insulator, and how the cable is constructed. Low-capacitance cables are usually thicker than standard cables and can be found where high-end stereo equipment is sold.

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USB and FireWire interfaces can be used to connect to external sound cards that are virtually immune to electrical noise from your computer (Figure 3-6). Because they move the digital-to-analog conversion outside of your computer, they are good choices for notebook computers that do not have line-out jacks. External sound cards can also provide more input and output jacks and mixing controls than most internal sound cards. See Chapter 2 for descriptions of several USB and FireWire sound cards that work well for audiophiles, DJs, and musicians.

Figure 3-6: USB audio connection to stereo

Some notebook computers omit the line-out jack in order to save space. If you still want to attach a notebook computer to an external stereo, you can use the headphone jack at the expense of some minor distortion. If your notebook has a knob or slider to control the headphone volume, start with it about one fifth of the way up to minimize distortion. A better solution for notebooks is to use an external sound card, such as the Edirol UA-3FX, that connects to the notebook's USB port (see Chapter 2).

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Several manufacturers, including RCA and X10, offer wireless audio devices that can transmit a stereo audio signal up to 300 feet. These devices use either the 900-MHz or 2.4-GHz spectrums, which are also used by cordless phones and wireless video cameras.

Most wireless audio transmitters include dual RCA jacks that can be connected to a sound card's line-out jack with a splitter cable. Most wireless audio receivers have dual RCA jacks that can be connected to a stereo receiver with a standard RCA interconnect cable (male-to-male RCA).

Some wireless audio devices are capable of delivering good sound quality, but interference from portable phones and other electrical devices can be a problem in heavily populated areas. Moreover, devices that use the 2.4-GHz spectrum can interfere with many wireless networks.

Wireless audio transmitters can be purchased for under $100, but you are much better off spending a little more for a wireless digital media receiver (more on that in a moment). These devices use standard wireless network protocols and can transmit higher-quality sound than wireless audio systems (Figure 3-7). A wireless connection between your computer and stereo system gives you the flexibility to transmit music from your computer to multiple rooms. Digital media receivers that use "wi-fi" network protocols provide the best quality sound and the most flexibility.

Figure 3-7: Wireless audio

Devices that use the 2.4-GHz spectrum can cause interference with 802.11b/g wireless networks. This is one of the reasons many people are returning to using 900-MHz cordless phones.

Wi-fi (short for wireless fidelity) is a popular term used to refer to wireless networks that use variations of the 802.11 specification. The 802.11b technology operates in the 2.4-GHz range with speeds up to 11 Mb/sec and is widely used for home networks. 802.11g is a newer specification that offers speeds up to 54Mb/sec. Devices that use 802.11b can communicate with 802.11g networks, but they will limit the network to the speed of the slower protocol. The 802.11a protocol is limited to short distances and is not commonly used for home networks.

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So, you don't want to run cables and you also don't want to interfere with your wireless hot spot or your cordless phone. A digital media receiver lets you use a network (wired or wireless) to transmit audio from your computer to receivers throughout your house. Most digital media receivers let you control music playback on your computer with a remote control, which can also be programmed to control your stereo receiver. Some digital media receivers include small built-in displays, while others rely on your television set.

A network connection provides the advantage of handling the digital to analog conversion outside of the noisy environment inside a typical computer, and it eliminates the interference, hum, and loss of high frequencies typical of analog cables and wireless audio connections.

Home networking has come down in cost and is fairly easy to install. Today, you can set up a small home network for well under $200. Besides allowing you to stream audio to any room in your house, a home network allows you to share an Internet connection and transfer files between computers.

Options for home networking include wireless (the least expensive and most flexible option, but subject to security issues) and dedicated wiring (more expensive and less flexible, but with much better security). The range of wireless networks is limited to about 150 feet, which should not be a problem in most homes.

Digital media receivers are relatively new products, and there is almost no standardization. Don't assume a receiver has any features other than those listed in the specification provided by the manufacturer. Many of the current products will not work with encrypted music files purchased from online music stores, but this capability is likely to be added to future models.

Table 3-5 shows several digital media receivers that can be purchased for under $300. The models with "RJ45 only" in the Wireless column require a wired network connection or an external wireless access point. Figure 3-8 shows the Squeezebox wireless digital audio receiver by Slim Devices (

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Once you have your music collection on your computer, you gain an enormous amount of flexibility and control. You have instant access to any song, and you can organize your music in ways that were not previously possible. Your CD player, tape deck, turntable, and all of the equipment that a DJ uses for mixing music are replaced by software on your computer. If someone has a request, or you want to change the music to match the mood, you can do it in seconds with a few mouse clicks. You can even configure some programs to choose songs based on your personal music tastes and to automatically crossfade between songs.

This chapter covers the basics of organizing and playing music with iTunes, Media Jukebox, and Musicmatch Jukebox. You will learn how to import downloadable songs, navigate your music collection, and create custom playlists, as well as how to master features such as automatic crossfading and volume leveling so that you can go head to head with any DJ. You will also learn about the options for customizing your jukebox program with skins, visualization effects, and remote controls.

You can download most jukebox programs for free. Some, including Media Jukebox and Musicmatch, sell "plus" versions that offer additional features, such as faster CD burning, the ability to print CD jewel case inserts, and advanced features for organizing your music. Table 4-1 shows the web sites where you can download the jukebox programs covered in this book.

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There are several options for acquiring and storing music on your computer. The easiest way is to download songs from a web site, online music store, or peer-to-peer network. Another option is to convert your existing records, tapes, and CDs into a compressed format such as MP3. Figure 4-1 illustrates these methods, and we cover each one in depth later in the book.

Figure 4-1: Obtaining music

However you acquire music, it helps to understand the differences between the various formats for digital audio. Following are descriptions of the most common formats and file types (we'll cover digital audio formats in much more depth in Chapter 9):

MP3: A compressed audio format that's part of the MPEG family of standards. MP3 is currently the most widely used format for downloadable music.
AAC: A very high quality compressed audio format that's part of the MPEG family of standards.
M4A: File extension for copy-protected AAC files downloaded from the iTunes Music Store.
M4P: File extension for unprotected AAC files created with iTunes.
Real Audio: A proprietary compressed audio format used by many Internet radio stations.
WMA: A proprietary compressed audio format developed by Microsoft.

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Jukebox programs use databases that allow you to organize and access your music collection in many different ways. For example, you can browse your collection by artist to display all songs by a particular artist, regardless of the genre, or you can browse by genre to display all songs within a certain genre, regardless of the artist.

In addition to the music, each audio file can contain metadata (related information, such as the song title, artist name, and album title). The place in the file where the metadata is stored is called a tag (see the "Metadata Tags" sidebar). The tag contains a field for each category of information (artist, album, etc.).

When you import songs into a jukebox program, metadata from each file's tag is read and stored in a database, which is called a music (or media) library. The fields from the tags are displayed as columns and/or folders that allow you to sort and browse the library. The music library contains additional metadata, such as the last time the song was played, that is not stored in the file's tag. Optional fields, such as rating, tempo, and mood, often exist in the library database, but not in the tags of individual songs.

Digital formats such as MP3 and WMA have the ability to store text and graphics within the file, in addition to the audio. The place in an MP3 file where this data is stored is called an ID3 tag. In a WMA file, it's called a WMA tag. Tags should include, at the very least, the song title, artist name, album title, and genre (type of music). If you purchase and download songs from an online music store, this information (and sometimes the album artwork) will already be embedded in the files. If you obtain a song via a file-sharing program such as Kazaa, this information may not be in the file, or the information might be incorrect, depending on who created the file.

With a program such as MoodLogic, you can automatically add the correct information to ID3 tags. MoodLogic maintains a massive online database that can match data (such as artist, song title, and year of release) with most songs. However, more obscure recordings—such as those you transfer from records rather than audio CDs—may not be in the database. If this is the case, you can always enter the information manually.

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Songs on your computer are stored as individual files, in one of a variety of formats (.mp3, .wav, .wma, and so on). The player software needs to "open" a file to play it. You can select songs or playlists from within your jukebox program, or you can select them from Windows Explorer or the Mac Finder.

The jukebox programs covered in this chapter give you several options for playing songs and playlists. Most of them allow you to play a song either by double-clicking it or by highlighting it and then clicking the "Play" button in the player window. The differences between these programs are more apparent in the way they handle playlists, which we will discuss momentarily.

To play a digital audio file (or playlist file) from Windows Explorer or the Mac Finder, just double-click the filename. If the player program is not already running, the system will launch the program associated with the file type (more on that later) and then play the file.

The player section of each jukebox program has buttons for common options, such as Play, Pause, Next Track, and Previous Track. In both iTunes and Media Jukebox, the "Play" button morphs into a "Pause" button once a song starts playing. When the song is stopped, the button then morphs back to "Play." Nearby are a volume control and a slider that shows the track's progress. You can drag the progress indicator to move forward or backward in the song.

Jukebox players have several modes. Loop and Repeat modes play the same song or playlist over and over again. Random (sometimes called Shuffle) mode plays songs in a random order, rather than in sequence. This feature is nice if you have a playlist with hundreds of songs, because it keeps you from getting bored by hearing the songs in the same order every time.

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A playlist is a list of songs to be played in a certain order. Playlists can be used like tapes, but without the limitations of recording songs onto physical media (time-consuming, high cost, limited capacity, difficult to make changes).

Creating and managing playlists is one of the most important functions of your jukebox program. Without some way to automatically feed the player program with one song after another, you would have to sit at your computer and select each song at the time it was to be played. With a jukebox program, you can easily create a playlist that contains hundreds of songs in a just few minutes. It would take you dozens of hours to record the same songs on cassette tapes, plus you would have to buy all those blank tapes!

Playlists are normally stored within your jukebox program's music library. Many jukebox programs allow you to export playlists from the library and import playlists created by other programs. Unfortunately, there are so many incompatible formats for playlists that it's not a simple matter to share playlists between programs. For most people, it's much faster and easier to print out each playlist and then manually recreate it in the other program.

Services like Napster 2.0 (see Chapter 5) and MoodLogic allow you to share playlists with other users via the Internet. Only the lists are shared; the songs cannot be downloaded from other users.

You can have as many playlists as you want, with as many songs as you like in them. The same song may appear in multiple lists, or multiple times on the same list. Playlists can even contain a mix of audio file types, as long as the player software supports them.

You might want playlists for specific occasions, such as parties or weddings. You might like to have playlists for certain types of music (classical, '60s rock, jazz, etc.). Or you might want playlists for certain situations (dance music, romantic music, easy listening) or for certain moods (broken-hearted, energetic, mad as hell). Your imagination, music collection, and musical tastes are the only limiting factors.

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