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.
4.3 COMFORT NOISE PAYLOAD FORMAT
As explained in the previous section, two popular types of VAD/CNG schemes are included in G.711. The noise power levels in both VAD/CNG methods are expressed in −dBov to interoperate with each other. The unit “dBov” is the dB level relative to the overload of the system. It is not a Volts reference for dBV. For example, in the case of μ-law-based coding, the maximum sine wave signal power without distortion is 3.17 dBm with amplitude ±8159. Square wave power is 3 dB more than sine wave power. The maximum possible power of signal from a square wave with an amplitude of ±8159 is 0 dBov as reference, which corresponds to a 6.17-dBm power level in the μ-law system. Hence, 0 dBov = 6.17 dBm is used in μ-law system. Sine and square wave power levels and signal amplitudes are shown in Fig. 4.1(c). Representation relative to the overload point of a system is particularly useful for digital implementations, because one does not need to know the relative calibration of the analog circuitry.
Figure 4.1. VAD/CNG representations. (a) VAD/CNG operation with G.729AB built-in VAD/CNG. (b) VAD/CNG with external VAD/CNG. (c) Power-level mapping with sine and square wave. (d) 1-byte power payload. (e) 11 bytes of payload.
Noise power levels in VAD are comparable from −40 to −60 dBm. The noise power is represented as −dBov with input power ranging from 0 to −127 dBov. ...
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.