Bitcrushing in plain English
Digital audio stores a sound as a long list of numbers called samples, usually 44,100 or 48,000 of them every second. Each sample says how far the speaker should be pushed at that instant, and the bit depth decides how finely that distance can be measured. A 16-bit file has 65,536 possible values for every sample, so the steps between them are far too small to hear.
A bitcrusher throws most of those values away. Set it to 4 bits and only 16 levels are left, so each sample gets moved to whichever of the 16 is nearest. The waveform that used to curve smoothly now jumps from step to step. Every jump leaves a small error, the difference between where the sample should be and where it was forced to go, and that error is what you hear as bitcrushing.
The control has different names in different plug-ins: Bits, Bit depth, Resolution or Bit reduction. Most bitcrushers also have a second control that lowers the sample rate, which is a separate effect with its own sound. It gets its own section further down.
Bit depth, levels and decibels
Every bit doubles the number of levels. One bit gives you 2, four bits give 16, eight bits give 256 and 24 bits give more than 16 million. The useful part is what each doubling does to the error.
An extra bit halves the size of the steps, so the rounding error gets half as big, and half the size is about 6 dB quieter. That gives the rule of thumb: each bit is worth about 6 dB of clean range between the loudest sound a file can hold and the error underneath it. 16-bit audio has about 96 dB of it, 8-bit about 48 dB and 4-bit about 24 dB. The lab measures the same thing on its 110 Hz test sine and gets 97 dB at 16 bits, 49 dB at 8 and 26 dB at 4, slightly better than the rule, because the textbook figure for a sine near full scale is 6.02 dB per bit plus another 1.76 dB.
The steps are spread evenly from silence up to full scale, which has a side effect on quiet sounds. Anything smaller than half a step rounds to zero. At 4 bits half a step is 1/16 of full scale, or −24 dBFS, so a fade or a reverb tail that drops under that line stops dead. Every bit you add moves the line 6 dB lower.
| Bits | Levels | Clean range | Rounds to silence below | What you hear |
|---|---|---|---|---|
| 16 | 65,536 | about 96 dB | −96 dBFS | No difference from the original |
| 12 | 4,096 | about 72 dB | −72 dBFS | A faint grain on fades and tails |
| 8 | 256 | about 48 dB | −48 dBFS | Clear grain on quiet parts, loud parts mostly intact |
| 6 | 64 | about 36 dB | −36 dBFS | Rough and noisy all through, still recognisable |
| 4 | 16 | about 24 dB | −24 dBFS | Heavy grit, tails cut off |
| 2 | 4 | about 12 dB | −12 dBFS | Only the loudest moments survive, as buzz |
Input level and bit depth
A bitcrusher's steps are fixed against full scale, so a quiet sound simply has fewer of them to use. A sound peaking just under 0 dBFS reaches every level the crusher has. Say a vocal peaks at −18 dBFS and goes through a 6-bit crusher: its loudest moments only get 4 steps above zero, so it lands on 9 of the 65 levels the lab's crusher has at 6 bits, close to what 3 bits would do to a loud vocal.
The rule of thumb is that every 6 dB quieter costs the sound about one bit. That's why the same setting can sound subtle on a mastered drum loop and wreck a quiet pad. Logic Pro's Bitcrusher has a Drive control that sets the gain going in, and with any other crusher you can turn the sound up in front of it and back down after it. The lab's Input knob does both halves for you: it turns the sound down before the crusher and back up after it, so the loudness stays put and only the number of steps in use changes. At 0 dB every sound peaks at about −1 dBFS, your own files included, so they all start with nearly the full range.
What does bitcrushing sound like?
It depends on how loud the sound is at each moment, which is why bitcrushing can sound like several effects at once.
On loud, held notes the error repeats with every cycle of the wave, and anything that repeats with the note is heard as harmonics. A bitcrusher rounds the top and bottom of the wave in the same way, so on a pure tone it adds odd harmonics only. A soft clipper's harmonics get quieter as they go up. A bitcrusher's can get louder, because each step is a sharp corner and sharp corners are made of high frequencies: at 3 bits the lab measures the 3rd harmonic at −37 dB, the 5th at −31 dB and the 9th as high as −26 dB. That rising row of high harmonics is the fizz on top of crushed synths and drums.
Many of those harmonics land above half the sample rate, where digital audio can't hold them, so they fold back down as aliasing, tones that have nothing to do with the note. On the harmonic screen they're the grey bar, at −32 dB on the 3-bit sine. On real music, with many notes and a level that keeps changing, the error stops lining up with any one note and comes out as a grainy noise. It's there while the sound plays and gone the moment it stops, which makes it very different from tape hiss.
Then there's the bottom of the range. As a note fades it falls through fewer and fewer steps and gets rougher, and once it's under half a step it rounds to zero and disappears. On drums that sounds like the decay of each hit being gated off. On a vocal you hear the words breaking up at the ends of phrases.
Reading the lab
The lab on this page has two cards, the bitcrusher and the downsampler. Drive and Character are greyed out because they only work on the analogue-style curves from the saturation page. Input sets the level going into the bitcrusher, and Bits sets how many steps it has.
The whole-loop screen shows the input in pale grey and the crushed output in green. At 4 bits, more than half of the drum loop comes out silent, because the tails of the hits are quieter than half a step. Those tails are too small to see at this size, so hover over a gap between hits: the readout gives the input level next to an output of −∞. The close-up shows 2 ms around the loudest peak, one dot per sample, and at low bit depths you can count the rows the dots sit on. The transfer curve turns into a staircase, with one step for every level.
The bitcrusher in this lab rounds to the nearest step and counts zero as one of them, so it has one more level than the round number: 17 at 4 bits, which is the figure the panel by the transfer curve quotes. That extra level is what lets silence stay silent. A real 4-bit file has 16, with one step fewer above zero than below it.
The harmonic screen runs the same settings on a 110 Hz sine and shows what was added, and the spectrum compares the loop before and after. The text panel by the transfer curve measures how far the error on that sine sits below the note. A/B switches the effect off, and Auto gain keeps the crushed and clean versions at the same loudness so the comparison is fair. You can also upload a file or record eight seconds of your own, and it loops through the lab in place of the built-in sounds.
Softening a bitcrusher with tone and mix
Raw bitcrushing is harsh because so much of the error sits high up. A low-pass filter after the crusher, which is what the lab's Tone control is, removes the sharpest part of that fizz and leaves the grain lower down. Somewhere between 4 and 8 kHz is a good place to start. On the 5-bit chords, the crusher leaves the loop with about 17 dB more energy above 3 kHz than the original, and closing the tone to 5 kHz brings that down to about 13 dB. The text panel by the transfer curve gives both figures as you move the knob.
The mix control does more. At 35% the clean sound carries the notes and the crushed copy only adds texture. That copy is now about 9 dB quieter, and so is everything it added: in the lab the grey bar on the harmonic screen falls from −46 to −55 dB. The quiet parts stop dropping out too, because the clean signal is still there when the crushed one rounds to zero. This is parallel bitcrushing, and if your crusher has no mix knob you can get the same result with a send to a separate channel.
Bitcrushing and sample rate reduction
Ableton Live's Redux and Logic Pro's Bitcrusher both have a bit depth control and a downsampling control, and the two get mixed up because they share a plug-in. They change different things. Bit reduction changes how many levels each sample can have, while sample rate reduction changes how often the sound is measured, by holding each sample for longer before taking the next one.
Quiet material shows the difference best. A bitcrusher wrecks quiet sounds first, because they have the fewest levels to use. A downsampler treats quiet and loud the same, and its damage depends on pitch instead: everything above half the new sample rate folds back down as metallic tones that are out of tune with the music. On the lab's transfer curve the downsampler is a straight line, because it never changes the level of a sample, only when it gets updated.
Used together they give the sound people associate with old digital gear, with grain from the bits and ringing from the rate. The sample rate reduction lesson covers the downsampler properly, and bitcrushing vs sample rate reduction puts the two side by side.
Bitcrushing, lo-fi and old samplers
Low bit depths weren't always a choice. Memory was expensive in early digital samplers, so the Fairlight CMI Series I and II and the Ensoniq Mirage recorded at 8 bits. The E-mu SP-1200 drum machine worked at 12 bits and 26.04 kHz, and its gritty drums are a big part of the sound of late-80s and 90s hip hop. Early game consoles were coarser still; the triangle wave on the Nintendo NES steps through just 16 levels.
A bitcrusher alone won't make your track sound like one of those machines. Their character also came from their converters and filters, and from the way people pitched samples up and down on them, which is why plug-ins that copy a specific sampler model those parts as well. Lo-fi as a style works the same way. It usually stacks a low-pass filter, some noise or vinyl crackle, a little pitch wobble and some saturation, with bitcrushing as one ingredient among them.
How to use a bitcrusher, step by step
- Start high and come downBegin at 12 bits and lower it until you can hear the grain, then keep going until it sounds the way you want. Most useful settings sit between 8 and 4 bits.
- Set the level going inMake sure the sound peaks close to 0 dBFS when it reaches the crusher, with a gain plug-in in front if you need one. Every 6 dB below that costs about a bit, which is what the Input knob in the lab shows.
- Filter the fizz after itPut a low-pass filter after the crusher, between 4 and 8 kHz, or use the plug-in's own tone control.
- Blend it inPull the mix down to between 20 and 50%, or put the crusher on a send, so the clean sound keeps the notes clear and covers the dropouts.
- Keep the low end cleanOn bass and kick, crush a copy and high-pass that copy at around 150 Hz, so the sub stays smooth and only the upper harmonics get grit.
- Compare at the same loudnessSwitch it off and on with the levels matched, and listen to the part in the full mix as well as soloed.
Starting settings for common sounds
These are places to start, picked so the crusher is clearly doing something. The input level changes everything, so set that first.
| Source | Bits | Other settings | What you get |
|---|---|---|---|
| Drum bus | 6–8 | Mix 20–40% | Grit and density on every hit, with the clean signal keeping the tails |
| Snare or clap | 4–6 | Low-pass at 6–8 kHz | A crunchier, older-sounding hit |
| Synth lead | 5–8 | Add some downsampling | The edge of an old game console |
| Chords and keys | 8–10 | Low-pass at about 5 kHz | A dusty texture for lo-fi parts |
| Vocal | 6–8 | On a send, high-passed at 200 Hz | Radio-style grit under the clean vocal |
| Bass | 6–8 | On a copy, high-passed at 150 Hz | An edge that reads on small speakers, over a clean sub |
Common bitcrushing mistakes
Crushing a quiet sound
If a part turns to noise and then cuts out, it was probably arriving at the crusher at too low a level. Turn it up before the crusher and down again after, or add a couple of bits.
Crushing the sub
A held 40 Hz note through a 4-bit crusher becomes a stepped wave for its whole length, and the sub turns into a buzz with none of its old weight. Crush a high-passed copy instead and leave the low end alone.
Putting the reverb in the wrong place
A crusher cuts off quiet tails, so a reverb in front of it gets chopped short and grainy. That can be a good effect on drums, but if you wanted a smooth tail, move the reverb after the crusher.
Judging it soloed
A crushed part that sounds great on its own can fill every gap in the mix with grainy noise. Listen to it with everything else playing, and try the mix control or a send before you reach for fewer bits.
Training your ears to hear bitcrushing
The quiz under the lab plays the current sound through either the bitcrusher at 5 bits or the downsampler at 3 kHz, with the screens covered and the levels matched, and asks which it was. Listen to the ends of notes. The bitcrusher turns the quiet parts to grain and then cuts them off, while the downsampler leaves the quiet parts alone and puts a metallic ring above every note. Try it on the chords first.
Questions people ask
What's the difference between a bitcrusher and a downsampler?
A bitcrusher lowers the bit depth, so each sample has fewer levels to choose from, and the result is grain and noise that follow the level of the sound. A downsampler lowers the sample rate, so the sound is measured less often, and the result is metallic, out-of-tune tones above the notes. Many plug-ins called bitcrushers do both.
How many bits sound lo-fi?
At 10 to 12 bits you mostly hear a faint grain on fades and reverb tails. At 8 bits that grain is plain on anything quiet while loud hits stay mostly intact, by 6 bits the crunch is on everything, and at 4 bits or fewer the quiet parts disappear and only the loud moments come through, as buzz.
Why does my sound cut out when I bitcrush it?
Anything quieter than half of one step rounds to zero. At 4 bits that's everything under about −24 dBFS, so fades, reverb tails and quiet notes stop dead. Turn the sound up before the crusher, or use more bits.
Is bitcrushing the same as exporting at a lower bit depth?
It is the same rounding. Exporting at 16 bits puts the error about 96 dB below full scale, and dither turns what is left into a faint, even hiss you will almost never hear. A bitcrusher goes down to 8 bits or fewer on purpose, so the error becomes part of the sound.
Does bitcrushing make the file smaller?
No. The plug-in still outputs audio at the bit depth of your session, usually 24-bit or 32-bit float. It only limits which values the samples are allowed to take, so an exported file comes out exactly the same size.
Should a bitcrusher go before or after reverb?
Put the reverb after the crusher if you want the tails to stay smooth, because a crusher cuts quiet tails off. Put it before the crusher when you want the reverb itself to turn grainy and chop off, which can sound good on drums.