Re: The best MP3 VBR bitrate choice when encoding audio?

industrial_one@xxxxxxxxxxx wrote:

Congratulations on the ear upgrade.

1. Does the choice of frequency (e.g. 44100) significantly affect the
bitrate, and vice versa? If so, is 48 KHz really necessary for most
songs?

It depends on the data content. If there is high frequency sound (cymbals, etc., anything over 11khz or with recorded harmonics over 1khz that mp3 isn't taking care of completely), then if you can hear that stuff, then you will be able to tell the difference. Whether it is necessary depends on what you want to hear.


2. Are there any disadvantages to using Variable Bit Rate when
encoding?

It may take a little longer to encode, but generally it "does the right thing" when encoding audio: low-content audio gets fewer bits than high-content audio (where 'content' is more or less 'more non-modeled frequencies').


3. Does constantly re-encoding the audio *** its quality up --
especially when switching from constant bit rate to VBR?

If you have 56kbit.mp3 -> wav -> 96kbit.mp3, you aren't gaining anything in the transition except for taking more space. Once you have lossey encoded data to a low bitrate, there is *no way* to get that data back. Find some .wav (optimally by ripping it yourself) with the proper features, or if you can't get it any other way, starting out with an mp3 of higher bitrate than what you want to end up with and reencode with that. It won't have as high a quality as if you started out with a wav, and hard drive space is cheap ($90 for 300 gigs), so I would suggest just downloading with bitrates at least as high as you want to listen and not bothering to reencode.


4. How do I know the bit rate I've chosen is ideal? By which I mean:
when I encode at 160 kbps and the output MP3 results with an average
of 137 kbps, was this the right choice? And when I encode at 144 I get
132. Which of these is the better choice?

If you give it more bitrate and it uses more bitrate, then it needed more bitrate (or thought it did) to accurately represent the sounds. If you can tell (heck, even if you cant, and you want people to listen to music with you), and you have the extra space, go with the higher quality stuff (though you will tend to get the best quality by not reencoding from a source mp3, and only starting from CD or some other losslessly encoded audio; like FLAC, Monkey lossless, etc.).


Most of the time the average bitrate was lower than the target bitrate
set, does it mean I have picked an ideal range? I tried to encode the
same song to 64 kbps once and I got 70 kbps instead. My guess is that
if the output bitrate was higher than the target, it means more bits
were required than chosen and the encoder was straining to keep the
quality while at the same time trying to satisfy the demand to be more
or less 64 kbps.

Generally yes, but for the sake of processing time, it may be only making one pass over the data, which makes it more or less impossible for it to correctly distribute bitrates through the song to produce your desired output size. If there were multiple pass variable bitrate encoding (like you see in movie encoding), you could get the bitrate more or less exactly what you want. Then again, a 10% over-bitrate isn't that bad.


5. Is 96 kbps good enough for general purpose audio instead of 128? I
notice no difference between the two, with some exceptional fast-paced
songs with high hypervarying frequencies.

If you can tell the difference with your ears, then it is likely that others can hear the difference with theirs. I personally can tell the difference in quality between 64, 96, 128, and 196 even with poor quality headphones, so I usually go for 196 or better.

If you friends can tell the difference, and you want them to listen to music with you, use higher bitrate (or just use the higher quality stuff from their ipods, etc.).


- Josiah
.

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