MP3 help

[biferi]

I need some help understanding something about mp3 encoding?

I have a WAV File it is 44.1 kHz Stereo 16 Bit and then I encoded it as MP3 98 kbps so it is now 368 KB in size this is ok.

Then I made one other but first I changed it from 16 Bit to 8. Bit and the 44.1 kHz to 2250 kHz and then encoded this one as MP3 98 kbps but this one also came out to the same size 368 KB?????????????????

I thought since I changed the audio first and then encoded it it would even be smaller.

Why the same size???

 

[Kage]

If I'm thinking correctly, your still encoding at 98kbps, so it'll be outputting the same kb's per second as the first file, regardless of what is actually on it

 

[Remeniz]

Yea. The encode rate is 98kb/s. So this means that every second of the encoded audio will be made up of 98 thousand bits.

It doesn't matter what the audio was before, if you want a reduced compressed audio file then reduce the encode rate further.

 

[J03]

Slightly off topic, but I went to an Open Day last Wednesday (at Cardiff). They had a talk about MP3 Compression - It's very interesting. They can cut certain tone's out because other tone's which are being "played" at the same time stop you from hearing other's... ish.

 

[Remeniz]

Slightly off topic, but I went to an Open Day last Wednesday (at Cardiff). They had a talk about MP3 Compression - It's very interesting. They can cut certain tone's out because other tone's which are being "played" at the same time stop you from hearing other's... ish.

Yea your right.

MP3 algorithms do some weird things to audio. The end result tries to keep what audibly 'should' be there as opposed to what was there but wasn't necessary.

This includes most content above 17Khz. You can see this with a high-res audio spectrum analyser.