Bitcrushing

Lowering bit depth and sample rate are two different moves, one adds grain, the other aliases.

Related

Bit DepthHarmonicsThe software synthesizer

The question

A bitcrusher lowers both bit depth and sample rate, producing coarse grain and mirror frequencies. It sounds like an old game console, but the two moves do different things.

How it works

Bit depth sets the quantization step size. At 8 bit the theoretical signal-to-noise ratio is about 48 dB, so quiet detail falls between steps. Lowering the sample rate folds content above Nyquist back as images, and sample-and-hold turns the waveform into stairs. Fewer bits give granular noise; a lower rate gives a metallic edge and aliasing. Anti-alias before decimating for a cleaner result; direct decimation leaves images in the high end.

Settings and what you hear

Dropping bits from 16 to 8 is obvious, and below 4 bit suits effects. Dropping the rate from 44.1 kHz to 8 kHz removes air and brings images back. Mix sets the parallel amount; on drums, 20 to 30 percent reveals the grain.

What to listen for

On an 8-bit battle cue, listen to the square lead, lower the bits and hear quiet notes turn sandy. At 8 kHz, hear cymbals turn into metal filings. On a clean piano, the same setting chops the decay into steps.

Common misconceptions

That bitcrushing accounts for all lo-fi; that lowering bit depth and lowering sample rate are the same; that adding it automatically sounds retro.

Sources

• Curtis Roads, The Computer Music Tutorial, quantization sections — background checked, not quoted
• Udo Zölzer, DAFX — Digital Audio Effects, bitstream processing chapter — background checked, not quoted

Used for fact-checking only; all prose is original.