How to tell if a CDR is MP3-sourced

Frequency Analysis

Most MP3 encoders out there cutoff the higher frequencies, so if we examine the audio frequency using a audio frequency spectrum analyzer we should see this. Be aware that that FM/TV and Mini Disc also suppress the higher frequencies.

Here are examples of spectral view for a few sources. A spectral view let you see the power in the frequency domain (Y axis) as a function of time (X axis). With CoolEdit [Menu "View" / "Spectral View"], the power is indicated with color. The more abundant a frequency (the greater a signal's amplitude component within a specific frequency range), the brighter the display color. Colors range from dark blue (next to no frequencies in this range exist) to bright yellow (frequencies in this range are very strong). Lower frequencies are displayed near the bottom of the display, and higher frequencies are displayed near the middle or the top.

A normal CDR should have some information for all frequencies in the range 0 to 22kHz. A MP3-sourced CDR will display a pretty clear cutoff before 22kHz (around 17kHz for 160kbps).

Tests with "About A Girl" from 06/18/91, the MP3 were created with mkw Audio Compressin Tool (which uses BladeEnc).

Other frequency-challenged formats:


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