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rsub8 | all galleries >> Live Music >> The Go-Betweens '85 >> measurement comparisons > 3. Spectrogram comparison of vinyl and CD.
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3. Spectrogram comparison of vinyl and CD.

This is the final piece of information confirming that the vinyl master is not sourced from the CD master.

The spectrogram shows frequency along the vertical axis and time horizontally.
Energy is indicated by the false-color scale, extending from -110 dB (black) to
-10 dB (white) below digital full scale. (The amplitude scale for the CD was offset
by 7 dB to compensate for the different overall recording level).

This transient, caused by a percussion instrument at about 13 seconds into the track,
shows high frequency energy that occurs at frequencies above the cut-off for CD recording
(22.05 kHz). If the vinyl master were produced from the CD master, information above 22.05 kHz
would be absent (except for vinyl background noise).

(note: this is not a vinyl "pop" or "click," which would have a much narrower profile. Besides,
the LP only has been played once - to transcribe it to a high resolution digital archive,
used for later playback, and for this analysis.)

Note that the frequency range of the spectrogram extends to 96 kHz. (The CD track was upsampled to 24 bit,
then sample-rate converted to 192 kHz for the comparison).

This also shows that the music was at least mastered digitally. If analog tape recording equipment
were used for mastering the vinyl, the tape bias (an ultrasonic signal present in all analog tape recordings)
would be visible in the spectrogram (it would appear as a faint, straight line running horizontally across
the spectrogram at a fixed frequency above about 30 kHz). Of course, if analog tape recording
equipment were used elsewhere in the recording chain, it may or may not be evident,
depending on the sample rate employed downstream by digital equipment (a high sample rate would
be needed to preserve the bias signal).

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