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Topic: Low Bitrate - Explainable? (Read 1740 times) previous topic - next topic
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Low Bitrate - Explainable?

I am converting a number of uncompressed WAV files to 320 AAC VBR Q 127 using Foobar.

The WAV files vary. Some are WAV files straight from a CD. Others are from unknown sources (possibly recordings). I find that the bit rates when examined in MP3tag, and just right clicking in Windows Explorer, vary all over the place. Some shows in the high 200's, some show under 100.

So my question is what possible reasons would a WAV file that is converted in Foobar in this fashion end up with such a low bitrate being displayed, or wildly varying bitrates?

Thanks.

Re: Low Bitrate - Explainable?

Reply #1 –
Since you're using VBR Q 127, I assume you're using qaac/CoreAudio to do the encoding, and Q 127 indicates you're using TVBR mode. In this mode, the encoder analyses the input to determine how much bitrate is needed to reach the selected quality setting, and the bitrate is free to vary accordingly. Music might take 320 kbps, whereas speech would potentially be around 224 kbps at TVBR 127 (the highest setting).

You say some of your input files are from "unknown" sources, which I assume means they could be bootlegged in any number of fashions. They could be mono, which would potentially cut the bitrate requirements in half alone, and they could have been through multiple other lossy encoding passes already that removed most of the original information, and thus they don't require as much bitrate as music that came straight from a CD. If the files aren't yours, there's no way for you to know what might have happened to them in the past.

If you don't want the bitrate to vary as much, you can use CVBR mode instead of TVBR mode to force a minimum bitrate threshold, but that won't necessarily yield any increase in quality. It'll just give you bigger files.
 

Re: Low Bitrate - Explainable?

Reply #2 –
Thank you very much for the fast and knowledgeable answer.

I was just using the default setting for the highest VBR for AAC in Foobar.