Re: [dispatch] [AVT] Proposal to form Internet Wideband AudioCodec WG
"Michael Ramalho (mramalho)" <mramalho@cisco.com> Mon, 20 July 2009 18:28 UTC
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Date: Mon, 20 Jul 2009 14:20:29 -0400
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Thread-Topic: [AVT] [dispatch] Proposal to form Internet Wideband AudioCodec WG
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From: "Michael Ramalho (mramalho)" <mramalho@cisco.com>
To: "DRAGE, Keith (Keith)" <drage@alcatel-lucent.com>, Dan York <dyork@voxeo.com>, dispatch@ietf.org
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Subject: Re: [dispatch] [AVT] Proposal to form Internet Wideband AudioCodec WG
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Keith, Comments in-line w/MAR: Regards, Michael A. Ramalho, Ph.D. -----Original Message----- From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] On Behalf Of DRAGE, Keith (Keith) Sent: Thursday, June 04, 2009 6:01 AM To: Dan York; dispatch@ietf.org Cc: avt@ietf.org Subject: Re: [AVT] [dispatch] Proposal to form Internet Wideband AudioCodec WG I would argue that G.711 is implemented, not because anyone can implement it, but because everyone else has implemented it. It essentially forms the lowest common denominator for interoperability. If fancy codec x doesn't work, then assuming you have the bandwidth availabile, G.711 probably will. And I suspect it is royalty free not because it was always so, but because any IPR that existed has pretty much expired by now. G.711 is also the one codec that is probably the most neutral to transcoding. I can do to codec A to G.711 and back to codec A with less impact that with any other intermediate codec. MAR: Let's look at that statement. G.711 is a simple *waveform* codec that achieves a (single frequency) SNR of approximately 25 dB over an approximate 25 dB dynamic range. The reason why you can "go to G.711 and back" is simply that the other (narrowband) codecs you use have less fidelity (i.e., on average much more distortion - or equivalently lesser SNR). The distortion introduced by G.711 is less than the distortion already introduced by the other codecs. MAR: An equivalent statement is that for the 0 - 4kHz band (narrowband), 25 dB SNR is good enough for telephony. For wideband there probably is not any one codec that has achieved that position. MAR: Well, the game changes with VOICE when it comes to wideband. Speech has a spectral tilt to it - lesser power per Hz with increasing frequency (as it comes from a finite energy acoustic source - this MUST be the case in the limit). The end result is that a PSD for an ensemble of speech signals has approximately 6dB less energy per octave (i.e., over all phonetic content). MAR: If you use G.711 for wideband (16k sampling) - the higher frequencies will have more distortion (i.e., much less than 25 dB). Thus G.711 sounds somewhat bad in wideband application due to this. MAR: What I believe you are asking for is: 1) a simple "waveform codec", 2) but one that is "pre-equalized" to whiten the spectral tilt in speech signals. For example, virtually all filter-band-based codecs (e.g., MLT/MCT-based) do this via the "bit allocation" process (sometimes in conjunction with pre-emphasis). MAR: I believe most of the codecs proposed for this proposed "codec" working group are speech-model based. If you want a "waveform based" solution that you can "transform into and out of" (something which I call a "do-no-harm" codec property) - you simply need pre-equalization plus a relatively simple waveform codec behind it (G.711 or something nearly as simple). MAR: Note these codecs will be less bandwidth efficient than the usual (model-based) suspects - as the model-based codecs generally only parameterize the spectrum (NOT the waveform) above 4kHz. But give me 60~90 kbps ... and such a codec becomes a relatively easy task for any signal processing graduate student (at least one that would have me on their thesis committee). MAR: Lastly, waveform based codecs are generally better for speech recognition applications - a quality that we might also desire to consider. I don't believe building a better, even royalty free codec, will guarantee a position in the market place. The world is littered with better solutions that never made it. You need a market where everyone chooses to implement it so that you can use that codec without having to go to transcoding. Pasting IETF on the front cover does not achieve that. I don't really have a problem with people trying to sit down and design a new codec and IETF then publishing it. Without some other selling point however it just becomes yet another codec competing for market place. As such, put it somewhere where it does not interfere with other work. Sticking it on a separate mailing list, and not letting it compete for valuable IETF face to face slots as a working group is fine. regards Keith
- [dispatch] Proposal to form Internet Wideband Aud… Jason Fischl
- Re: [dispatch] Proposal to form Internet Wideband… Eric Burger
- Re: [dispatch] Proposal to form Internet Wideband… Roni Even
- Re: [dispatch] Proposal to form Internet Wideband… Scott Lawrence
- Re: [dispatch] Proposal to form Internet Wideband… Henry Sinnreich
- Re: [dispatch] Proposal to form Internet Wideband… Jason Fischl
- Re: [dispatch] Proposal to form Internet Wideband… Roni Even
- Re: [dispatch] Proposal to form Internet Wideband… Spencer Dawkins
- Re: [dispatch] Proposal to form Internet Wideband… Roni Even
- Re: [dispatch] Proposal to form Internet Wideband… Henry Sinnreich
- Re: [dispatch] Proposal to form Internet Wideband… Joel M. Halpern
- Re: [dispatch] Proposal to form Internet Wideband… Henry Sinnreich
- Re: [dispatch] Proposal to form Internet Wideband… Roni Even
- Re: [dispatch] Proposal to form Internet Wideband… Mary Barnes
- Re: [dispatch] Proposal to form Internet Wideband… Gonzalo Camarillo
- Re: [dispatch] Proposal to form Internet Wideband… Eric Burger
- Re: [dispatch] Proposal to form Internet Wideband… Cullen Jennings
- Re: [dispatch] Proposal to form Internet Wideband… eburger
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Roni Even
- Re: [dispatch] Proposal to form Internet Wideband… Slava Borilin
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Jean-Marc Valin
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Henry Sinnreich
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Roni Even
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Henning Schulzrinne
- Re: [dispatch] [AVT] Proposal to form Internet Wi… James M. Polk
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Spencer Dawkins
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Slava Borilin
- Re: [dispatch] [AVT] Proposal to form Internet Wi… stephen botzko
- Re: [dispatch] [AVT] Proposal to form Internet Wi… stephen botzko
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Joel M. Halpern
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Henning Schulzrinne
- Re: [dispatch] [AVT] Proposal to form Internet Wi… stephen botzko
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Henry Sinnreich
- Re: [dispatch] [AVT] Proposal to form Internet Wi… David Singer
- Re: [dispatch] [AVT] Proposal to form Internet Wi… David Singer
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Randell Jesup
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Slava Borilin
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Eric Burger
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Eric Burger
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Jean-Marc Valin
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Dan York
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Joel M. Halpern
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Henry Sinnreich
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Jason Fischl
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Dean Willis
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Christopher Montgomery
- Re: [dispatch] [AVT] Proposal to form Internet Wi… DRAGE, Keith (Keith)
- Re: [dispatch] [AVT] Proposal to form Internet Wi… Michael Ramalho (mramalho)