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Audio File size reduction
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Jedi Knight
Picture of Andrew
posted
Hi,

I have some audio files that I need to distribute and want to get them into a form that will require minimum bandwidth.

I assume I can do this within iTunes using "Convert to mp3".

What settings do you recommend I use? The audio is of a recorded teleconference, so the quality is not that great (or important) to begin with... A small file size is.

I'm also open to suggestions other than iTunes.

Thanks in advance for your help!

Andrew :-)
 
Posts: 152 | Registered: December 21, 2002Reply With QuoteReport This Post
iBBS Addict
Picture of macjeff
posted Hide Post
If your audio file is only spoken word then you might want to consider setting the bit rate to 96kpbs or less ( using iTunes and the mp3 format )

If 96kpbs still makes a too large file....then try 64kpbs


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Posts: 1796 | Location: Washington, Michigan | Registered: June 29, 2002Reply With QuoteReport This Post
Jedi Knight
Picture of Andrew
posted Hide Post
Thanks for that Jeff.

Not only is it spoken word, it's spoken word over the telephone.

I'll try as you've suggested.

Also, can anyone tell me the difference between "Stereo Bit Rate" and "Sample Rate"?

What effect do each have on quality and file size?

Thanks,

Andrew :-)
 
Posts: 152 | Registered: December 21, 2002Reply With QuoteReport This Post
Jedi Master
Picture of arrakian
posted Hide Post
More bits and higher rates = better sound quality. A sample rate of 22k, and a 24 kbps (with or without VBR) should be a small, nice-sounding file.


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Posts: 1360 | Location: S.E.MI | Registered: June 22, 2002Reply With QuoteReport This Post
Poobah
Picture of Chuck M
posted Hide Post
The phone company only transmits sound between 300 Hz and ~3000 Hz. For voice, 8 bit samples would be adequate. There's a 2X Nyquist sampling factor. So, 8*3000*2= 48000 kbps. Not surprisingly, that's just under the bit rate that dial up V.90 modems use (the old "56K" modems). This number is for a monophonic connection. Stereo bitrate would be twice the mono rate, but phone conversations aren't transmitted in stereo.

The sample rate must be at least 2X the highest analog frequency to be transmitted. The minimum sample rate must be 6000 Hz in this case.

So, you'll waste Internet bandwidth and download time if you go too much above 48kbps. You can try 64kbps if 96kbps is too big. I wouldn't think file size is a big consideration here; sound quality should predominate.
 
Posts: 2075 | Registered: June 23, 2002Reply With QuoteReport This Post
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