Audio CD Quality Check - Tau Analyzer, AuCDtect (Win, Linux)

Many music lovers wondered about the quality of their recordings. And their concern is not unreasonable, instead of a full-fledged Audio CD, you can often get razzatka with mp3. This unloading sounds different, because when compressed, the audio signals are not transmitted accurately, the cutoff frequency decreases. In Audio CD, for example, the maximum signal frequency is about 22 kHz, for mp3s with a constant bit rate of 160 kbps, only about 16 kHz.

Bad Audio CDs can make audio pirates, as getting the original disk image for replication is harder than finding someone rip. The near distributors of losslessly compressed tracks (ape, flac) can do the same, if instead of taking the original disc as the source, they took a pirated disc or stupidly converted their mp3 files to flac.

But not everyone wondered how such records could be distinguished. They differ by ear from the original, but it is difficult to determine which of them is the original and which ones are unloading. Audiophiles tend to get the sound as close as possible to the original. To help such people, the Tau Analyzer program was created.

Tau Analyzer is a program for determining the authenticity of tracks on a CD. Based on the presence of lossy compression in the artifacts, the program makes an assumption about what the source is - the original studio recording or unloading from mp3.

The program interface is very simple. It is enough to insert a disk and press the “Analyze CD” button on the left. In a few minutes we will get a decision on each track and on the disc as a whole. As a pleasant and useful addition, you can see the spectrogram and frequency response of each track.

Overview

To illustrate the work of the program, we take two discs: a licensed disc of the Splin publishing house Sony Music and a no less licensed disc of the GDR group of the publishing house Real Records. The screenshots below show the frequency response of the songs "New People" and "Jonathan" from the first and second discs, respectively.


Spleen - "New People" of the


GDR - "Jonathan"

Tau Analyzer recognized the first disc as original (CDDA), and the second as unloading (MPEG). Sound from the second disc seems undetailed and “jammed”.

AuCDtect and testing

AuCDtect is a console program designed for similar purposes and implementing the same algorithm. Easy to use, there are versions for windows and linux. For analysis, this program takes wav files.

In order to check the program’s work, I removed the track “New People” from the disk and saved it as a wav file. Then it was alternately compressed using:

lame 3.98b8 mp3 codec with cbr 128, cbr192, extreme, insane presets; oggenc ogg codec with quality 7aac neroaacenc codec with quality 0.6
After that, the received files were again decompressed into wav and fed to AuCDtect . In normal accuracy mode, AuCDtect made a mistake only on the uncompressed aac file - it was mistaken for CDDA. In maximum accuracy mode AuCDtect did not make a single mistake!

Thus, Tau Analyzer and AuCDtect prove to be useful and reliable programs for music lovers.

Terms Used

Unzipping - creating an Audio CD image from rip.
Rip - saving tracks from an Audio CD to files on a hard drive, usually occurs with an irreversible loss of some information, i.e. decline in quality.

References

True Audio Codec Software
Tau Analyzer version 1.2 (Windows)
AuCDtect version 0.8 (Windows)
AuCDtect version 0.8 (Linux x86)
AuCDtect version 0.8 release 3 (Linux rpm)

PS My first habit :)