September 2008
Intermediate to advanced
550 pages
18h 10m
English
Content preview from VoIP Voice and Fax Signal ProcessingBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
3.4 G.726 OR ADPCM COMPRESSION
G.726 is an ITU-T-G.726 recommendation (1990) known as ADPCM. This waveform-based compression does not assume any vocal tract models [URL (Cisco-coding)]. It works on a sample basis by making use of a short-term correlation of samples. ADPCM is used in PSTN for overloaded digital circuit multiplication equipment (DCME) channels. In DCME, more T- or E-carrier channels are multiplexed on the same digital channels. Cordless and DECT phones use ADPCM for communication between the base station and multiple cordless units. A modified version of ADPCM is used in wideband G.722 [ITU-T-G.722 (1988)] with two sub-bands that deliver a higher quality than PSTN. In packet voice, G.726 was initially included in voice over asynchronous transfer mode (VoATM). In the migration of VoATM to VoIP, several compression codecs were considered that provide comparable quality at a lower bit rate than G.726. Hence, G.726 is not preferred in many VoIP deployments. In some VoIP-to-PSTN voice gateways, G.726 is supported for better interoperability.
ADPCM is easy to implement on dedicated chips. The processing is mainly through arithmetic and logical operations than through multiplications. The codec takes about 7 to 8 million cycles per second (MCPS) processing on a single multiplier accumulator-based generic digital signal processor (DSP) like TI-54x [URL (TI-54x)] and ADSP-218x [URL (ADI-218x)], which occupies much lower memory when compared with low-bit-rate codecs.
3.4.1 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.