Vorbis - Oct 2002 - RE: Hlp in finding a native Ogg trim, fade & nomalise tool

Hi John

A trimer/vcut type application is possible but unfortunately not a
fade/normaliser.  Not without decoding/encoding.  I asked about this a
couple of years ago.  Unlike MP3, the Ogg Vorbis format doesn't store a
global gain setting per frame.

I have often downloaded MP3 files from mp3.com and other sources for
broadcasting, and with the type of music I need, it is often not
normalised before encoding so I find it very useful to be able to
normalise the volume of the MP3 file without losing quality.  It is a
shame that in the future when Ogg Vorbis is the codec of choice, I'll
have to re-encode.  

Hopefully some more work can be done to reduce the artifacts from
re-encoding.

Ross Levis
WinVorbis & Vorbix v1.40 (just released)
http://winvorbis.stationplaylist.com
> > From: John K Muir <jkmuir@trentu.ca>
> > Subject: Help in finding a native Ogg trim, fade & nomalise tool
> > 
> > My specific interest lies in a project which involves the digital 
> > ingest of about 13,000 CDs, 8000 LPs and various and sundry 
> other tape 
> > and disc formats into a online intranet resource for programmers at 
> > non profit community radio facility.
> > 
> > The tests of the codec were very satisfying, and for all 
> the reasons 
> > spelled out on the http://www.vorbis.com site. We are 
> excited at the 
> > prospect of using a non-proprietary codec in our non-profit 
> > organisation.
> > 
> > Our problem is that we really want to get it as good as we can the 
> > first time around. While we do plan on keeping all the audio 
> > materials, once an item is digitised, we hope it will be a 
> long time 
> > before the original is dug up and re-encoded. And we 
> believe it would 
> > be wise for us to avoid "transcoding" if at all possible.
> > 
> > The rough outline of the plan is to use Win98SE with 
> Audiograbber and 
> > the Ogg codec system to make analogue recordings and rip the CDs .
> > 
> > The resulting ogg and associated files (meta date, such as  text &
> > graphics) will reside on a network attached server, with 
> perhaps a SQL 
> > application running on an independent  cpu to handle searches from 
> > other workstations on the LAN.
> > 
> > The one tool which doesn't seem to exist yet for the Ogg 
> format is the 
> > equivalent of something like MP3Trim,  
> > http://www.logiccell.com/~mp3trim/
> > which provides a convenient method of trimming,  
> normalising and fading MP3 files
> > with the need to decode and reencode.  I have tried VCut, 
> but it behaved in a way
> > which I did not understand, and did not seem to work at all 
> with a Variable Bit
> > Rate
> > Ogg file.
> > 
> > I would very much appreciate finding out if there is such a 
> tool which 
> > can be used
> > 
> > like MP3Trim, or if someone is working on one.
> > 
> > I know there are number methods to trim and normalise a wav 
> file prior 
> > to it being encoded, but its would be better to be able to 
> manipulate 
> > audio once it is the ogg format as well.
> > 
> > Without this tool or some hope that some method to provide these 
> > functions will come into being in the next few months, we 
> will not be 
> > able to commit to the Ogg format.
> > 
> > Would it be any incentive to announce that we would we would make a 
> > donation
> > ($100)
> > to the Xiph.org Foundation and tell our listeners to to do 
> the same, while
> > producing and
> > airing radio programmes about the work of the foundation?
> > 
> > All the best // John
> > 
> > http://www.trentradio.ca
> > 
> > 
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Ross Levis wrote:
> I have often downloaded MP3 files from mp3.com and other sources for
> broadcasting, and with the type of music I need, it is often not
> normalised before encoding so I find it very useful to be able to
> normalise the volume of the MP3 file without losing quality.  
I'm confused.  Ross, your software supports ReplayGain.  Do you find it 
inadequate?


-- 
-:-:- David K. Gasaway
-:-:- XNS  : =David K Gasaway
-:-:- Email: dave@gasaway.org
-:-:- Web  : dave.gasaway.org

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On 2002-10-02, Ross Levis wrote:
> Hi John
>
> A trimer/vcut type application is possible but unfortunately not a
> fade/normaliser.  Not without decoding/encoding.  I asked about this a
> couple of years ago.  Unlike MP3, the Ogg Vorbis format doesn't store a
> global gain setting per frame.
>
I think this:

http://www.xiph.org/archives/vorbis-dev/200105/0139.html

comes from the thread which you refer to but it's the part which was
crossposted to vorbis-dev where some more detailed answers were given.
Look for the following messages by Monty and Segher...  To sum up, there
actually is a per-frame volume in Vorbis (but twiddling it might be a bit
complicated and no tools were ever written for this) and the volume of the
whole stream can be changed by very easy codebook manipualtion (it might
have become less easy with the introduction of channel couplig).  The
later (amplifying the whole stream) is now implemented in ReplayGain by
most self-respecting vorbis players so there is no need for the codebook
manipulation anyway...
> I have often downloaded MP3 files from mp3.com and other sources for
> broadcasting, and with the type of music I need, it is often not
> normalised before encoding so I find it very useful to be able to
> normalise the volume of the MP3 file without losing quality.It is a
> shame that in the future when Ogg Vorbis is the codec of choice, I'll
> have to re-encode.
>
>From following messages I understand that you don't just want to
normalize
(== scale the whole sound) but to compress it (== variable scaling
depending on local volume average).  The first is already done by
ReplayGain well.  The second is best achieved by player tricks (like
ReplayGain with extra amp and a limiter or generic compression plugins).
I don't quite see the reason for compressing the vorbis file itself (even
if it was lossless) since compression generally lowers audio fidelity.
Store the vorbis file as is and compress before playing through media
requiring it (like FM).

However (read above thread), there is a theretical possibility to
losslessly manipulate volume locally in Vorbis.  The only problem is that
the envelope is defined with packet granularity (somewhat smoothed by the
window function).  This will make the envelope sort of "wavy" which
might
distort the frequency domain (any modulation does but this adds
higher-frequency componenets to the envelope than usually).  I'm don't
know whether this can introduce audible distortions with typical
fade-in/out transition lengths; I suppose it would be OK.  I don't fill
very good about doing it all throughout the song (for compression) - but
you'll need somebody more knowledgeable than me to clarify this....
> Hopefully some more work can be done to reduce the artifacts from
> re-encoding.
>
Another trick once suggested for fade in/out at ends of the pieces (or
even cross-fading) is to reencode only the ends and copy the middle as-is.
This should leave the degradation almost unnoticable.  Obviously it
doesn't solve compression but why do you want it?


-- 
Beni Cherniavsky <cben@tx.technion.ac.il>

Awake! Awake! Fear, Fire, Foes! Awake! Fire, Foes! Awake! [Tolkien, LOTR]
Fight software patents:  http://lpf.ai.mit.edu/
BTW, does somebody know what's the situation in Israel
concerning software patents?

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