A test signal has to be exact. This writes one directly as PCM, so the file contains the waveform that was asked for rather than a codec’s approximation of it.
Shapes
Sine holds a single frequency and nothing else. It is the signal for calibration, level matching, and checking whether a chain is distorting.
Square carries the odd harmonics at 1/3, 1/5, 1/7 of the fundamental’s amplitude. Feeding one through a filter shows the filter’s slope in a way a sine cannot.
Triangle also carries odd harmonics but they fall away much faster, so it is a softer version of the same test.
Sawtooth carries every harmonic, odd and even, which makes it the fullest signal here and the standard starting point for subtractive synthesis.
Frequency and sweeps
A steady tone stays where you put it. 1 kHz is the reference frequency for level work, 440 Hz is A4, and 20 Hz to 20 kHz brackets the audible range.
A sweep moves from the start frequency to the end frequency across the whole duration. Phase is integrated from the instantaneous frequency rather than recalculated, so the sweep stays continuous with no discontinuity at any point in it.
Choose logarithmic for anything acoustic. It gives each octave equal time, which matches how both hearing and room behaviour are distributed.
Level
Level is peak amplitude in dBFS. -6 dBFS leaves headroom for whatever the signal passes through; 0 dBFS is full scale and will clip anything that adds gain after it.
For lining up two pieces of equipment, a 1 kHz sine at -18 dBFS is the common studio alignment level.
File settings
Sample rate limits what can exist in the file: nothing above half of it. At 8 kHz a 5 kHz tone is impossible, and asking for one produces an alias, not a tone.
Bit depth sets the noise floor: about -96 dBFS at 16-bit, -144 at 24-bit. For a test signal that will be measured, 24-bit is the safer choice.
Example: checking a speaker for rattle
Logarithmic sweep, 20 Hz to 20 kHz, 30 seconds, -12 dBFS, mono.
Play it through one driver at a time and listen for anything that continues after the sweep has moved past. A slow sweep makes a buzz easy to locate by frequency.