Killer Game Programming in Java

Sampled Audio

Sampled audio is a series of digital samples extracted from analog signals, as illustrated by Figure 7-3. Each sample represents the amplitude (loudness) of the signal at a given moment.

The quality of the digital result depends on two factors: time resolution (the sampling rate), measured in Hertz (Hz), and amplitude resolution (quantization), the number of bits representing each sample. For example, a CD track is typically sampled at 44.1 kHz (44,100 samples per second), and each sample uses 16 bits to encode a possible 65,536 amplitudes.

Descriptions of sampled audio often talk about frames (e.g., frame size, frame rate). For most audio formats, a frame is the number of bytes required to represent a single

Figure 7-3. From analog to digital audio

sample. For example, a sample in 8-bit mono pulse code modulation (PCM) format requires one frame (one byte) per sample. 16-bit mono PCM samples require two frames, and 16-bit stereo PCM needs four frames: 2 bytes each for the left and right 16-bit samples in the stereo.

As the sample rate and quantization increase, so do the memory requirements. For instance, a three-second stereo CD track, using 16-bit PCM, requires 44,100×4×3 bytes of space, or 517 KB. The "4" in the calculation reflects the need for four frames to store each stereo 16-bit sample.

The higher the sample rate and quantization, the better the sound quality when ...