Glenn Parsons (gparsons@nortelnetworks.com)
Wed, 29 Nov 2000 11:48:02 -0500
I'm not sure if it is a qualitative judgement but G.711 and G.726 have long
been considered 'toll quality'. Most long distance voice trunking between
'toll offices' uses G.726.
The MOS of G.711 is 4.5 and of G.726 is 4.2 with no impairments. The
E-model is more often used now to estimate subjective MOS ratings. An R
value of 75 or greater (equivalent to a MOS of about 4 or better) is
generally viewed as 'toll quality'. G.711 has an R value of 91 and G.726
has an R value of 84 (both decrease with transcoding, but G.726 more so).
Glenn.
> ----------
> From: David Oran
> Sent: Wednesday, November 29, 2000 8:18 am
> To: vpim
> Subject: [VPIM] FW: I-D ACTION:draft-ietf-vpim-vpimv2r2-32k-00.txt
>
> <<File: ATT00408.txt>><<File: draft-ietf-vpim-vpimv2r2-32k-00.txt>>
> It would be much better to retitle this document simply as "32 kbit/s
> ADPCM MIME Sub-type Registration" and avoid qualitative judgments about
> what exactly does and does not represent "toll quality".
>
> In fact, I suspect this encoding does not in fact qualify for a MOS score
> of 4 which is the conventionally applied level for "toll quality". (I seem
> to remember it having a MOS of around 3.9 or 3.8 with no impairments but I
> could have my facts wrong)
>
> Dave.
>
> -----Original Message-----
> From: nsyracus@cnri.reston.va.us [mailto:nsyracus@cnri.reston.va.us]On
> Behalf Of Internet-Drafts@ietf.org
> Sent: Tuesday, November 21, 2000 5:58 AM
> To: IETF-Announce:
> Cc: vpim@lists.neystadt.org
> Subject: I-D ACTION:draft-ietf-vpim-vpimv2r2-32k-00.txt
>
>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories. This draft is a work item of the Voice Profile for Internet
> Mail Working Group of the IETF.
>
> Title : Toll Quality Voice - 32 kbit/s ADPCM MIME Sub-type
>
> Registration
> Author(s) : G. Vaudreuil, G. Parsons
> Filename : draft-ietf-vpim-vpimv2r2-32k-00.txt
> Pages : 6
> Date : 20-Nov-00
>
> This document describes the registration of the MIME sub-type
> audio/32KADPCM for toll quality audio. This audio encoding is
> defined by the ITU-T in Recommendation G.726. This document refines
> an earlier sub-type registration in RFC 1911.
>
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>
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