trixter http://www.0xdecafbad.com wrote:
On Sat, 2005-07-16 at 17:05 -0500, Michael Graves wrote:
I agree with others who have chimed in that IP-to-IP calls can sound
better than PSTN calls. I have a co-worker who has a SipGate account in
the UK. Calls to him via SipGate go out through my FreeWorldDialup
account. They sound great. So good that in silent moments we often
think that we've been severed, even with no silence suppression on the
line.
One thing that many PSTN providers are doing for calls when they went
digital is to insert small quantities of noise into the line. That way
people do not think they are disconnected. There is a bunch of
documentation on this, and even some that applies to VoIP
providers/equipment doing the same (its basically a faint bit of white
noise so you hear *something*).
It's sometimes called comfort noise... As far as I'm aware, it's only
done in VoIP.
I spent 15 years working with digital switches/T1 channel banks. I
guess it might have been built in and I just didn't know about it, but
we were very concerned about excess noise and quantization noise as it
was. We used to inject a 1004 test tone and then use a notch filter to
measure the amount of quantization noise at the reciever.
Just as a by the by, G.711ulaw is the codec used in channel banks.
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