Are bitcrushing and decimation the same thing?

No. Bit reduction lowers amplitude resolution and adds quantisation distortion. Decimation (sample-rate reduction) lowers time resolution and folds high frequencies back down as inharmonic aliasing. Most 'bitcrusher' plugins do both, but the two artifacts sound completely different.

Why does sample-rate reduction sound metallic?

Any content above half the new sample rate has nowhere to go, so it mirrors back into the audible band at frequencies that are not harmonically related to the source. That inharmonic foldover is the metallic sheen.

Which one should I use on drums?

Rate reduction first - it keeps transients readable while adding grit and sheen. Add mild bit reduction for crackle. A post filter tames the foldover when it gets harsh.

Tech Explainer

Bitcrusher vs Decimator

One breaks amplitude, the other breaks time. Crackle versus metal - and why vintage hardware needed both.

Two different kinds of damage

Producers say "bitcrusher" for both effects, but a crusher section actually contains two separate processes that break audio on two different axes.

Bit reduction lowers amplitude resolution. At 16 bits you have 65,536 possible levels per sample; at 8 bits, 256; at 4 bits, 16. Every sample snaps to the nearest available level, and the rounding error rides along as quantisation distortion - crackle at high bit depths, a fizzy, gated rasp by the time you reach 4 bits, and a square-ish growl at 1-2 bits.

Decimation - sample-rate reduction - lowers time resolution instead. The processor holds each sample value for N samples (a rate divide), which is why it is also called downsampling or sample-and-hold. The side effect is the signature: any frequency above half the new effective rate folds back into the audible band as aliasing - inharmonic partials that are not musically related to the source. That is the metallic sheen in every classic sampler and console soundtrack.

How each one sounds

Bit reduction: noise floor rises, sustain tails crackle and gate, character is fuzzy and gritty. Harmonically related to the source, so it stays musical fairly deep.
Rate reduction: highs disappear and are replaced by inharmonic foldover, transients stay surprisingly intact, character is metallic and cold. Pitch-dependent, so it changes flavor across the keyboard.
Together: the actual vintage-hardware sound. Old samplers and console chips had both a low sample rate and a small word size - one without the other reads as a modern plugin trick.

Doing it deliberately

The CRUSH ROM cartridge in TALLBOY lays the whole chain out in the open, which makes it a good way to learn the difference by ear:

BITS (1-16): start at 16 and walk down. Nothing changes until ~12, texture appears at 8, the source starts gating at 4.
RATE divide (1-64): at 44.1 kHz, a divide of 8 is an effective 5.5 kHz - everything above 2.75 kHz folds down. Add jitter and the hold time wobbles, which smears the foldover into hiss like aging hardware.
DRIVE into the quantiser: pushing level into the bit reducer changes which steps the signal hits - more drive means denser crackle, the cheapest way to make crush feel loud without being loud.
POST filter (18 kHz down to 540 Hz): the civilising move. Foldover above the cutoff disappears, and at the bottom of the range you get the small-speaker playback tone.

Bus trick: run CRUSH ROM fully crushed on a parallel return under the dry drums. You keep the transient truth of the original and rent the texture, which is how crush survives on otherwise clean mixes.

The short version

Bit reduction breaks amplitude; decimation breaks time. Crackle versus metal. Old hardware did both at once, which is why one alone never quite sounds vintage. TALLBOY's CRUSH ROM does both with jitter, drive and a post filter for $20 - and when you feed it something monophonic, the other two cartridges will resynthesize it into a genuine chip voice on top.

Hear the difference on real drums

The TALLBOY page has a drum loop through CRUSH ROM alone - rate first, then bits. Free demo, no email required.

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