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Groove Topology: Sine Wave

This article series analyses the geometrical representation of various signals when being cut/pressed onto a lacquer/vinyl record. It is meant to help understand the physical subtleties of the process.

Part one of the series starts by looking into the representation of pure sine waves on a disk record.

Also see:
Groove Topology: Clipped Sine
Groove Topology: Noise
Groove Topology: Sawtooth Wave

1 kHz Sine Wave, Mono, 33 1/3 rpm, 12″ outer

This groove was cut at a large radius, near the outer border of the disk. This is generally the most ideal situation, offering greatest resolution and the potentially lowest amounts of distortion when cut/tracked.

1 kHz Sine Wave, Mono, 33 1/3 rpm, 12″ inner

This groove was cut at a small radius, close to disk center. Note how much slower the tracking speed is, and how much more compact the geometry has to become to produce the same 1kHz Sine. In case of 12″, the tracking speed between outer and most inner groove shrinks 3 fold. A smaller playback radius generally produces denser, more demanding geometry than a larger radius.

1 kHz Sine Wave, Panned Left

Note that only the inner side of the groove (in this picture: the left side) is modulated, the outer (or right) side of it is practically featureless, i.e. silent.

1 kHz Sine Wave, Panned Right

Here, only the outer side of the groove is modulated, while the inner side remains flat.

1 kHz Sine Wave, Antiphase

In case of an anti-phase situation, i.e. one of both stereo sides having an inverted polarity, the signal translates into vertical movement. The groove purely moves up and down, observable by the modulated groove width and the straight groove center line.

Side Sweep, Antiphase

This antiphase sine sweep illustrates the fundamental issue behind excessive negatively correlated stereo being converted into a groove: The grooves literally act like ski jumps for badly configured pickup systems, potentially provoking excessive distortion during playback.

All animations made with the TDR SimuLathe REF/TDR SimuLathe CUT disk mastering simulator series.

Read next: Groove Topology: Clipped Sine

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