MP3 Encoding Question

chemistry_geek

chemistry_geek

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Does anyone know much about MP3 encoding? Or where I can find information on it? I just purchased the sound track to Artificial Intelligence (A.I.) and immediately noticed a huge difference in the MP3 compared to the actual recording, specifically in the low frequency range. Basically, I can barely hear the high amplitude low frequency bass on track 8 through $150 German headphones. Playing through my stereo, I hear nice tight bass. Does MP3 encoding automatically remove certain frequency ranges from music assuming the average consumer isn't likely to hear?

My encoding settings are:

320kbps stereo / 8kbps mono, Smart Encoding Adjustments is checked, Stereo mode is joint stereo, Sample rate is set to Auto.
 
MPEG 3 Audio uses a technique called "Psycho-acoustic redundancy" to remove sound information it considers to be beyond the range or perception of the human ear in order to minimise the file size once compressed.

This is the audio equivalent of JPEG compression for images. You know how JPEG images lack detail in some of the big, evenly coloured areas? That is because the compressor reads a block of the image, and if the contrast between the pixels is very low, it simply defines them as being the same.

MP3 encoding is very similar. If it percieves a change in sound to be insignificant, it disregards this in order to decrease file size. That is one of the reasons MP3 is so much smaller than any of the lossless audio compression techniques, by at least a factor of five.

MP3 is, therefore, not really suited to studio or production use. However, for the home user the sound is quite pleasing: almost (but not quite) as good as CDs. I tend to notice the difference only when I listen with my German studio headphones, and 95% of music will have no noticeable difference.

So, the bad news is that yes, you are right on about MP3 ditching certain sounds. I'd suggest you consider using another non-lossy audio format for this sort of music. You'll find some music genre will work great with MP3, and others, particularly high-definition orchestral music, will fall a bit short.
 
Thanks for the explanation. I already knew about the psycho-acoustic redundancy technique employed in MP3. I was just wondering if there was a way to change the encoding a little to leave in some or all of the frequency ranges I noticed were missing. What lossless audio compression exists out there? Will it work with iTunes?

BTW, the headphones I have are BeyerDynamic DT511 - bought them about 10 years ago at a professional audio shop.
 
I think this problem may have a little to do with the amplifier in my logic board. When I listen directly from the CD, the low frequencies are just a little better. It may not be the MP3 after all. I wish I had the specs for Apple's amplifier in their computers.
 
From what I've read, the built in QuickSilver amp is actually a very good one. Never used it in mine, though. I have SoundSticks :D

I'm not sure about the amp in older PowerMacs, though. :confused:
 
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