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).
- Normal CDR: notice the smooth transitions of blue in the high frequencies.
- 320kbps MP3: notice the abrupt transitions from blue to "nothing" in the high frequencies.
- 256kbps MP3: notice the abrupt transitions from blue to "nothing" in the high frequencies.
- 160kbps MP3: no doubt there! This is the typical MP3-Sourced show with a clear cutoff at 17kHz.
Other frequency-challenged formats:
- FM CDR ("About A Girl" from Trick or Treat). Compare with
160kbps MP3, there is still some power in the higher frequencies here... A frequency analysis
[Menu "Analyse" / "Frequency Analysis"] will tell you that the higher
frequencies are at -100dB as opposed to -120dB for the MP3.
- FM CDR ("About A Girl" from Roma).
Links
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