128 kbps compression

[rbnlife]

alright. Im doing some audio work for a company.. They want it in 128 kbps for some internet streaming stuff. What I want to know is if anyone has some actual data or charts or something (other then there opinions) on frequency correlations when compression occurs. For example... Is there a certain rage lost between 128 and 256? I understand it sounds a bit more squashed/muddy/however you wanna call it.. But i want to know the actual numbers and/or percentages of impedance occurring... Please, can anyone help.

Thank you for your time

Jordan

Ohh, if its any consolation, Im talking about bringing in a PRO TOOls 48kHZ recorded session, bounced to AIFF 24bit sample rate of 48000. Then importing to Itunes and converting to ACC 128kbps......

[StavrosSound]

Well, you can try importing the MP3 at different encoding rates to PT, and flip phase against the uncompressed. Whatever remains is more or less what was lost.

EDIT: My bad, just realized you wanted tangible data... Not sure there, you can try spectral analysis of the two since it'll break down the harmonic content, but other than that, I'm not exactly sure. Might be in the MP3 white papers if there are any available.