Re: [codec] Last proposal for the update draft

Felicia Lim <flim@google.com> Tue, 21 June 2016 09:22 UTC

Return-Path: <flim@google.com>
X-Original-To: codec@ietfa.amsl.com
Delivered-To: codec@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 2D23612D0B8 for <codec@ietfa.amsl.com>; Tue, 21 Jun 2016 02:22:38 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.126
X-Spam-Level:
X-Spam-Status: No, score=-4.126 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_LOW=-0.7, RP_MATCHES_RCVD=-1.426, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=google.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id b4rRpfg867Gm for <codec@ietfa.amsl.com>; Tue, 21 Jun 2016 02:22:34 -0700 (PDT)
Received: from mail-lf0-x22e.google.com (mail-lf0-x22e.google.com [IPv6:2a00:1450:4010:c07::22e]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id A310612D099 for <codec@ietf.org>; Tue, 21 Jun 2016 02:22:33 -0700 (PDT)
Received: by mail-lf0-x22e.google.com with SMTP id f6so14104276lfg.0 for <codec@ietf.org>; Tue, 21 Jun 2016 02:22:33 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=nutn09L4pIXZgYXmiNJ3geV4mQxUQUyWoa2DQ9cy12I=; b=PyBAlywJicbUa8UsEM65DI0fiW1m3ONUWR+ddf07U8X/UH9VZJv/LZ4qL4ZJKobHYO wpQiIeqckxw2z3Ddcib6FjPPN07jSoH9fOlBjTSnww3IHUrB66cdT149ToxTQKu/UJHn jlab8klktZOVc5uJpG+dJUFeEDCyEBirzW+Uc+lO98vO2cwOSKhmqoy5G3xYeek7+ElV vJUVbuqO4/Jxh22RnrLJX0LIPLI9WJ4wXFXlRILFSspUiCRbZcF1lVqEwAfQUW1PHpSf 6H97DhLArDG2GTNdMuMUN+z1D9A4Z5FjwZfTXL/y339ErHCBUrGilLuwSvbn5VdHNfl6 5bWw==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=nutn09L4pIXZgYXmiNJ3geV4mQxUQUyWoa2DQ9cy12I=; b=UKImgIV5k2Z9HcRwLI0bObXA4xVODNIWZodOtEu1A9uhHmIs8sqJe0HEnj5hLt7vy7 l7ft7HwxZq65T6rxnNgmcwGMc0OYmcYcMcju4LDNg0vEfPtJ9OmOkAPr0eom6pVeRXiK nReiJ/XW7W+ldu9JAUszaFPKswhnum+2C06DMNQRE4L/aBZMF2JTWn6SGYShow8nwNCd QLHmYeDUsJueks3pfnUjQqNupiHbRC9a8AoCHwlIvFdNfHQUCiqHm624NLSIyz8OxHiq lNM4HmzWuDuXmyTegTyzF+NstbhciaYxabwMwItHOTRsJNhcv+jFKVFIGmrkT5bE/Ozs bBPg==
X-Gm-Message-State: ALyK8tIQjQcSQu4VsLA28twqToH9jzl1bI4mCJ/hTlhPTXGklcE7MqOb4GuJYp69pBto+NCDddG6mVU1zejHiWGG
X-Received: by 10.25.85.75 with SMTP id j72mr6485024lfb.31.1466500951618; Tue, 21 Jun 2016 02:22:31 -0700 (PDT)
MIME-Version: 1.0
References: <d743fe38-a558-770d-9a23-2c37900b47ec@jmvalin.ca>
In-Reply-To: <d743fe38-a558-770d-9a23-2c37900b47ec@jmvalin.ca>
From: Felicia Lim <flim@google.com>
Date: Tue, 21 Jun 2016 09:22:22 +0000
Message-ID: <CAJ0LFHXmY4pCHPbqH8H4PVcUstvgpi=_DO081LHfp8S5dYntnw@mail.gmail.com>
To: "codec@ietf.org" <codec@ietf.org>
Content-Type: multipart/alternative; boundary=001a1140d8084907650535c65c56
Archived-At: <https://mailarchive.ietf.org/arch/msg/codec/n-9vYvl5pNvsdf3XPVbPnv9SWCk>
Subject: Re: [codec] Last proposal for the update draft
X-BeenThere: codec@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Codec WG <codec.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/codec>, <mailto:codec-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/codec/>
List-Post: <mailto:codec@ietf.org>
List-Help: <mailto:codec-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/codec>, <mailto:codec-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 21 Jun 2016 09:22:38 -0000

+1

On Fri, Jun 17, 2016 at 2:26 PM Jean-Marc Valin <jmvalin@jmvalin.ca> wrote:

> Hi,
>
> I've been working on completing the update draft and have come across
> one last thing that I think should be updated in the spec. This was
> discovered through running hybrid mode at low rates, around 16 kb/s.
>
> At those rates, we sometimes only have enough bits to code a single
> CELT band (8 - 9.6 kHz). When that happens in hybrid mode (unlike
> CELT-only), the second band (CELT band 18, from 9.6 to 12 kHz) cannot
> use folding because it is wider than the amount already coded, and
> falls back to LCG noise. Because it can also happen on transients
> (e.g. stops), it can cause audible pre-echo.
>
> My proposed solution is to fix the folding behaviour so that it is
> never forced to fall back to LCG due to not enough folding data. This
> is achieved by simply repeating part of the first band in the folding
> of the second band. The proposed patch is available at:
> https://git.xiph.org/?p=opus.git;a=commitdiff;h=949c7f33181
> It's a decoder-only change and it fixes the low-bitrate pre-echo
> problem. I uploaded a short example that demonstrates the problem and
> the fix. This is before the change:
> http://jmvalin.ca/misc_stuff/fix_before.wav
> and this is after the change:
> http://jmvalin.ca/misc_stuff/fix_after.wav
> Note especially the "t" in the word "tour", which has noticeable HF
> pre-echo in the "before" file. Both files are decoded from the same 16
> kb/s CBR bit-stream.
>
> The fix does not impact compatibility, because the improvement does
> not depend on the encoder doing anything special. I also do not see
> any case where an encoder could have effectively used the current
> broken behaviour to improve quality over the proposed change.
>
> For these reasons, I think it should be included in the update draft.
>
> Cheers,
>
>         Jean-Marc
>
> _______________________________________________
> codec mailing list
> codec@ietf.org
> https://www.ietf.org/mailman/listinfo/codec
>