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16 kbps for MP3 silent track?
Posted by: magicmikey
Date: June 08, 2010 08:24AM
I use a RF remote control to operate my iPod Nano for use in my magic shows. In order to keep the iPod from going to sleep, I use a 20 minute silent track between each musical track. When I first generated a 20 minute silent track with Audacity, the file was 19.4 MB in size. That seemed pretty large for silence!

I started experimenting today and figured out that I could reduce the file size tremendously by reducing the bit rate. When I went to 16 kbps, the file is only 2.5 MB. I can't hear any difference on my MacBook between the 19.4 MB file (at 128 kbps) and the 2.5 MB but I haven't tried it on my PA. This may be a stupid question but am I going to notice any difference by using such a low bit rate for a silent track? If not, is there any disadvantage to using 16 kbps?

P.S. I won't use that bit rate for the musical tracks. I'll keep them at the recommended 256 kbps. This is strictly for the silent track.

Thanks,
Michael
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Re: 16 kbps for MP3 silent track?
Posted by: mikebw
Date: June 08, 2010 08:29AM
Highly compressed silence should still be silent, you are just reducing the amount of information used to represent a flat line, but then I haven't ever tried doing that before so best to test it first.
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Re: 16 kbps for MP3 silent track?
Posted by: Ken Sp.
Date: June 08, 2010 08:59AM
The non-noise may attract dogs from blocks away. They will show up and silently bark......and you will know the end is near.
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Re: 16 kbps for MP3 silent track?
Posted by: magicmikey
Date: June 08, 2010 09:03AM
Quote
mikebw
Highly compressed silence should still be silent, you are just reducing the amount of information used to represent a flat line, but then I haven't ever tried doing that before so best to test it first.

That's what I'm thinking.

Quote
Ken Sp.
The non-noise may attract dogs from blocks away. They will show up and silently bark......and you will know the end is near.

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Re: 16 kbps for MP3 silent track?
Posted by: deckeda
Date: June 08, 2010 09:05AM
The static bitrate is the size of the available space regardless of content. That's why the file has to "weigh" something. Try remaking it as a mono track, or delete L or R from a stereo track if you haven't already, and it may be smaller yet.

Audacity will let you go down to an 8K sample rate, which will further reduce the file size (perhaps dramatically, compared to a standard 44K). A very low sample rate on the other hand, is where you may run into a noise issue, since sample rate has a direct influence on dynamic range and the noise floor.

Think of sample rate as the amount of noise, even for "digital black" and the bitrate as the quality of that noise. Mix and match to arrive at the best compromise, but remember that the iPod has a minimum sample rate it'll play (is it 32K ?) — and don't go by whatever iTunes will play. It relies on Quicktime, which can play a wider range of files than can an iPod.

In the end, whatever amplifier you listen through will probably have more hiss than the resulting file.



Edited 1 time(s). Last edit at 06/08/2010 09:06AM by deckeda.
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Re: 16 kbps for MP3 silent track?
Posted by: magicmikey
Date: June 08, 2010 06:16PM
Thanks for the info deckeda. I went ahead and generated a silent track at 8K bit rate and a 22K sample rate. This created a 1.3 MB file. That's small enough for me!

I tested it today and used it in a show and it worked fine.

Thanks,
Michael
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