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Compressing Audio for Web download

 
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Bill



Joined: 29 Nov 2007
Posts: 12

PostPosted: Tue Sep 16, 2008 9:20 pm    Post subject: Compressing Audio for Web download Reply with quote

I have an audio file that I wish to compress, so that the webmaster can upload it. It is speaking, about 20 minutes long, mono. I will upload it to my .mac account, and the webmaster will download it, and then upload it to her web page. It is the last step that times out for her. I have Amadeus Pro, Quicktime Pro, and Audacity. What is the best compression file type?
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CDJonah_alt



Joined: 15 Mar 2007
Posts: 378

PostPosted: Tue Sep 16, 2008 11:03 pm    Post subject: Compressing Audio for Web download Reply with quote

If you haven't done it, I would normalize to 100% absolute max (not rms)
and then run it through a compressor -- mda dynamics or the apple
version that has dynamics in it. (you do this after you save a master
version; you can do the normalize before saving it.) I have had good
luck with the mdadynamics but that only means I tried it in the early
days, it worked and so I didn't try it on anything else. I would then
save the file using mp3 and 40k. That should get the file down maybe a
factor of 30.

Other types of compression (AAC or Ogg for example) might be better but
everyone can handle mp3s.

Any of the programs should work fine.

Chuck

Bill wrote:
Quote:
I have an audio file that I wish to compress, so that the webmaster can upload it. It is speaking, about 20 minutes long, mono. I will upload it to my .mac account, and the webmaster will download it, and then upload it to her web page. It is the last step that times out for her. I have Amadeus Pro, Quicktime Pro, and Audacity. What is the best compression file type?

------------------------
Bill




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rfwilmut



Joined: 17 Nov 2006
Posts: 255

PostPosted: Wed Sep 17, 2008 8:36 am    Post subject: Reply with quote

Better still, just compress it using MP3 and don't use the MDA compressor unless you want it to sound as if you were being beaten round the head with an invisible newspaper. MDA applies dynamic audio compression - making the quiet bits sound as loud as the loud bits. This has no bearing on what the OP was asking about - reducing the file size for the web.

As said, though there are technically better systems, MP3 is absolutely universal. For a stereo file, 192kb/s will produce very reasonable results; 160kb/s is acceptable for a good deal of material; below that the quality will progressively deteriorate as you reduce the bitrate. Of course for mono files you can halve these rates. It's worth experimenting until you get the result you want.

In Amadeus's Save dialog you get a choice of various file types including MP3, and a Settings area to choose the bitrate. Choose 'best' quality - it's slower to compress but produces slightly better results.
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Bill



Joined: 29 Nov 2007
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PostPosted: Wed Sep 17, 2008 12:29 pm    Post subject: Reply with quote

That reduced my mono mp3 file from 35 Mb to 20 Mb, and I cannot hear any degredation. Excellent! Is there any reason to use stereo for web audio (speaking)? If not, would that change your recommendation?

Many thanks!
Bill
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CDJonah_alt



Joined: 15 Mar 2007
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PostPosted: Wed Sep 17, 2008 1:09 pm    Post subject: Compressing Audio for Web download Reply with quote

Actually, I disagree here -- I have found compression makes the spoken
word more easily listenable. I am quite aware that it doesn't change
the size of the file. (I don't compress music but I have found that
voice is generally improved in listenability). Your ear does a
fantastic job of auto volume control on live material; for some reason,
that is turned off when listening to a recording.

Chuck

rfwilmut wrote:
Quote:
Better still, just compress it using MP3 and don't use the MDA compressor unless you want it to sound as if you were being beaten round the head with an invisible newspaper. MDA applies dynamic audio compression - making the quiet bits sound as loud as the loud bits. This has no bearing on what the OP was asking about - reducing the file size for the web.

As said, though there are technically better systems, MP3 is absolutely universal. For a stereo file, 192kb/s will produce very reasonable results; 160kb/s is acceptable for a good deal of material; below that the quality will progressively deteriorate as you reduce the bitrate. Of course for mono files you can halve these rates. It's worth experimenting until you get the result you want.




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CDJonah_alt



Joined: 15 Mar 2007
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PostPosted: Wed Sep 17, 2008 1:12 pm    Post subject: Compressing Audio for Web download Reply with quote

and for voice, I find 40 khz will do a perfectly good job and no, there
is no good reason for stereo.

Chuck

Charles Jonah wrote:
Quote:
Actually, I disagree here -- I have found compression makes the spoken
word more easily listenable. I am quite aware that it doesn't change
the size of the file. (I don't compress music but I have found that
voice is generally improved in listenability). Your ear does a
fantastic job of auto volume control on live material; for some
reason, that is turned off when listening to a recording.

Chuck

rfwilmut wrote:
Quote:
Better still, just compress it using MP3 and don't use the MDA
compressor unless you want it to sound as if you were being beaten
round the head with an invisible newspaper. MDA applies dynamic audio
compression - making the quiet bits sound as loud as the loud bits.
This has no bearing on what the OP was asking about - reducing the
file size for the web.

As said, though there are technically better systems, MP3 is
absolutely universal. For a stereo file, 192kb/s will produce very
reasonable results; 160kb/s is acceptable for a good deal of
material; below that the quality will progressively deteriorate as
you reduce the bitrate. Of course for mono files you can halve these
rates. It's worth experimenting until you get the result you want.




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rfwilmut



Joined: 17 Nov 2006
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PostPosted: Wed Sep 17, 2008 5:18 pm    Post subject: Re: Compressing Audio for Web download Reply with quote

[quote="CDJonah_alt"]Actually, I disagree here -- I have found compression makes the spoken
word more easily listenable./quote]

Of course this is a matter of personal opinion. Personally, I hate dynamic compression, which people tend to apply willy-nilly: occasionally there is a need for it, when the voice levels are all over the place, but I dislike the all-too-obvious pumping effects. It should be applied very carefully, not as a matter of course.
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rfwilmut



Joined: 17 Nov 2006
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PostPosted: Wed Sep 17, 2008 5:21 pm    Post subject: Reply with quote

[quote="Bill" Is there any reason to use stereo for web audio (speaking)? If not, would that change your recommendation?/quote]

If a recording is in stereo, it should ideally be converted to a stereo MP3: if it's in mono )or even stereo where both channels are identical) then mono takes uip half the space. For straight speech mono is probably adequate unless you really want separate speakers to be positioned differently. The bitrates I quoted can of course be halved for mono, so 192kb/s stereo is exactly the same as 96kb/s mono.
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CDJonah_alt



Joined: 15 Mar 2007
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PostPosted: Wed Sep 17, 2008 5:34 pm    Post subject: Compressing Audio for Web download Reply with quote

Note that I said -- after making sure you have saved the unmodified!
And note, I am only talking about speech -- I have yet to resort to it
with music, and 95% of my work is with music. All I can say is that
when I use mdadynamics on _speech_, it has been more satisfactory (at
least to me and to others who have heard the difference). I just came
back from a seminar that would be totally unlistenable in a recording,
but easily understood at the time. I have blathered on previously on
music groups about the strange (at least to me) difference between how
the ear (or the eye) works in real life and reproduction.

Chuck

rfwilmut wrote:
Quote:
[quote="CDJonah_alt"]Actually, I disagree here -- I have found compression makes the spoken
word more easily listenable./quote]

Of course this is a matter of personal opinion. Personally, I hate dynamic compression, which people tend to apply willy-nilly: occasionally there is a need for it, when the voice levels are all over the place, but I dislike the all-too-obvious pumping effects. It should be applied very carefully, not as a matter of course.




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Charles D. Jonah CDJonah@anl.gov
630-252-3471
Chemistry Division
Argonne National Laboratory
Argonne, IL 60439



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rfwilmut



Joined: 17 Nov 2006
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PostPosted: Thu Sep 18, 2008 9:01 am    Post subject: Re: Compressing Audio for Web download Reply with quote

CDJonah_alt wrote:
I just came
back from a seminar that would be totally unlistenable in a recording,
but easily understood at the time.


This is exactly the sort of situation where it can help - some people mumbling and some speaking loudly.
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[/quote]
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Charles D. Jonah CDJonah@anl.gov
630-252-3471
Chemistry Division
Argonne National Laboratory
Argonne, IL 60439



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Gerard Bik



Joined: 10 Nov 2006
Posts: 353

PostPosted: Thu Sep 18, 2008 9:22 am    Post subject: Compressing Audio for Web download Reply with quote

Quote:
CDJonah_alt wrote:
Quote:
I just came
back from a seminar that would be totally unlistenable in a recording,
but easily understood at the time.


This is exactly the sort of situation where it can help - some people mumbling and some speaking loudly.
_____

The Levelator (see my earlier post) does a remarkably good job improving these situations.

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