make a recordHow Audio Becomes Record Grooves: Pitch, RPM and Capacity
Make a Record places audio samples along a spiral. Time advances as the disc rotates, while the spiral moves toward the centre. The audio either shifts the groove sideways or changes its depth.
How the audio is prepared
The converter selects a clip, mixes stereo to mono, low-pass filters the signal, resamples it to the groove's sample rate, and peak-normalizes it. Optional RIAA pre-emphasis compensates for the playback equalization of a phono preamp. Optional quantization reduces the number of amplitude levels.
The default low-pass cutoff is 40% of the groove sample rate. The preview WAV contains this conditioned signal. It is not a recording of a physical disc and does not predict its noise level.
What sets the groove sample rate?
The software uses a fixed number of points per revolution, so sample rate = points per revolution × RPM / 60. Unless explicitly overridden, the point count is based on the circumference at the outer program radius divided by the target segment length.
For the default 302 mm LightBurn disc, the outer program radius is 145 mm. A 0.1 mm target segment length gives approximately 9,111 points per revolution and a sample rate of about 5,062 Hz at 33⅓ RPM. The report gives the actual rounded values for each conversion.
What controls capacity?
Groove pitch is the radial distance between turns. The approximate number of program turns is the usable radial span divided by pitch, less the turns reserved for run-out. Playtime is program turns divided by revolutions per second.
A wider usable band or finer pitch increases theoretical capacity. Finer pitch also leaves less room for modulation and the physical channel. The validator checks that neighbouring grooves have enough separating material. STL output reserves additional spiral turns so the mesh retains space between its ending turns.
Lateral and depth modulation
Laser files and FDM STL presets move the groove sideways. The resin STL preset changes the depth of a V groove. The STL uses a 90-degree included angle by default; its width changes with depth. Increasing amplitude or groove depth can consume the land needed between turns.
Can a normal turntable play it?
The design targets ordinary turntable playback, but successful tracking depends on the fabricated channel, material, disc flatness, stylus, and cartridge. Select a supported playback speed and test on an inexpensive stylus. Expect experimental, limited-bandwidth audio rather than the fidelity of a pressed commercial record.
What is the difference between the preview and decode?
The browser preview is generated from the prepared audio before fabrication. The command-line decode function reads the encoded geometry from SVG or DXF to recover a signal. Neither includes the mechanical effects of a cutter, printer, or turntable. A physical playback recording is a third, separate measurement.
Method and further reading
This guide describes Make a Record's source code and presets. The broader technique follows earlier digital fabrication experiments, including Amanda Ghassaei's laser-cut records. Suggested fabrication settings need validation on your machine; they are not manufacturer-certified profiles.