Lower the bits when you want grit that stays in tune with the part, and expect it to eat quiet tails first. Lower the sample rate when you want the dull, metallic top end of an old sampler, and expect the new tones to clash with the key on melodic parts.
Most plug-ins called bitcrushers have both controls, and the old-sampler sound uses a little of each.
At a glance
| Property | Bitcrusher | Downsampler |
|---|---|---|
| What it lowers | Bit depth: the number of levels | Sample rate: the number of samples a second |
| The staircase it draws | Steps in level, at every sample | Steps in time, each held flat |
| Transfer curve | A staircase | A straight line |
| Depends on | How loud the sound is | How high its frequencies go |
| On a steady note | Harmonics, in tune with the note | Tones that aren't harmonics of the note |
| Top end | Kept, with fizz added over it | Replaced above half the rate by mirrored copies |
| Quiet parts | Turn grainy, then drop to silence | Come through at their own level |
| The clean version | Lowering bit depth with dither | Sample rate conversion with filters |
| Best for | Grit on drums and synths that stays in key | Old-sampler drums and phone-style voices |
What's the difference between bitcrushing and sample rate reduction?
Digital audio is a list of numbers called samples. Each one gives the height of the waveform at one instant, so every sample has two properties: when it happens and how high it is. The sample rate decides the first, usually 44,100 or 48,000 samples a second. The bit depth decides how finely the second can be measured, and a 16-bit file can put each sample on any of 65,536 levels.
The two effects each take one of those away. A bitcrusher keeps every sample at its proper moment and moves its height to the nearest of a few levels; at 6 bits there are 64. A sample rate reducer, usually called a downsampler or decimator, keeps every height exactly and throws away moments instead: it takes a sample, holds it flat for as long as a slower recording would have, then takes the next one. At 6 kHz in a 44.1 kHz session, each sample it takes is held for seven or eight.
Both turn a smooth wave into a staircase, which is why they get confused, but the steps run in different directions. The bitcrusher's steps are in level, so its transfer curve in the lab becomes a staircase. The downsampler never changes a level, so its transfer curve stays a straight line and all of its steps are in time. Look at the close-up of one peak in the lab and switch between the two cards: the crushed dots snap to rows, easiest to see where the wave is flattest, and the downsampled dots line up in flat runs of seven or eight.
Loudness against pitch
A bitcrusher's steps are fixed against full scale, so how much damage it does depends on how loud the sound is. A downsampler's steps are fixed in time, so its damage depends on how high the frequencies are. Turning a sound down changes nothing for a downsampler, and changing the pitch leaves a bitcrusher's staircase exactly as it was.
A bitcrusher rounds anything smaller than half a step to zero, and half a step at 6 bits is 1/64 of full scale, about −36 dBFS. Say a vocal peaks at −6 dBFS: it has 30 dB of room before it disappears, so breaths and word endings more than 30 dB below the peaks drop out. The same vocal peaking at −18 dBFS has only 18 dB of room and breaks up much sooner. Every 6 dB quieter costs a sound about one bit.
A downsampler at 6 kHz ignores all of that. Its limit is half the rate, 3 kHz, and anything above it folds back down as aliasing, whether it's a loud cymbal or a quiet breath. A bass line playing under 300 Hz keeps its notes and only its upper harmonics fold, while the sibilance in a vocal, mostly between 5 and 10 kHz, gets folded every time.
In tune or out of tune
Run a pure 110 Hz sine through each and the difference shows up on the harmonics screen. The bitcrusher's rounding error has the same shape on every cycle of the wave, and anything that repeats with the note is heard as harmonics, at whole-number multiples of it. Rounding treats the top and bottom of the wave the same, so they're odd harmonics: 330, 550, 770 Hz and on up. At 4 bits they get louder as they go up, from −51 dB at the 3rd to −42 dB at the 11th, and the row carries on well past the screen. The highest pass half the project's sample rate and fold back down, which is the grey bar at −36 dB. The Right now panel puts the whole error at 26 dB below the note, so about nine tenths of its energy is in harmonics of the note.
The downsampler adds nothing at those frequencies. Taking only a few thousand samples a second creates mirrored copies of the sound either side of the new rate and each multiple of it, and holding each sample flat, with a sharp corner at every step, lets those copies through. At a 3 kHz rate, the 110 Hz sine picks up tones at 2,890 and 3,110 Hz, then either side of 6 kHz, 9 kHz and on up. 2,890 Hz is 26.3 times 110, so it isn't a harmonic of the note, and you hear it as a ring that doesn't belong.
On a melody, aliasing adds more of the same. Say a downsampler at 8 kHz plays an A at 220 Hz. Its limit is 4 kHz, so the 19th harmonic, at 4,180 Hz, folds to 8,000 − 4,180 = 3,820 Hz, and the 20th, at 4,400 Hz, folds to 3,600 Hz. Each lands 80 Hz above a real harmonic of the note, where it clashes with the part, and on the next note the gap changes. That's why a downsampled lead sounds out of tune while a crushed one only sounds rough.
The top end
A bitcrusher keeps every frequency the sound had and adds its error on top, spread right up to 22 kHz. A downsampler throws away everything above half its rate and fills that space with mirrored copies of what's below it, while anything that was up there folds down among the notes. Both can leave more energy up there than before. On the chords, the lab's dB above 3k figure, which compares the energy above 3 kHz with the original at matched loudness, reads +13 dB for the bitcrusher at 6 bits and +16 dB for the downsampler at 6 kHz.
Those readings are close, but the crushed chords still have their own top end under the fizz and the downsampled chords have lost theirs. Hi-hats lose their air and vocals lose their sparkle, and the copies that replace them ring with a metallic edge. That loss is why a downsampled sound seems older and duller even when the meter says it has more top end.
The spectrum screen in the lab shows where the difference lies. Switch between the cards on the chords: on both, the coloured line follows the original through the low mids and then levels off into a raised floor above it. The bitcrusher's floor is smooth, an even layer of rounding error over the chords' own top end. The downsampler's is spiky, because it's made of mirrored copies of the notes below 3 kHz.
Filtering each one
A low-pass filter after a bitcrusher works well. Most of the harshness sits high up, so a filter between 4 and 8 kHz softens the fizz, and what it leaves underneath is grain and harmonics that still follow the notes.
After a downsampler, the same filter only removes the step buzz above the limit. The folded tones are already below it, among the real parts of the sound, where no filter can separate them. To get less aliasing you need a filter before the downsampler, set at or below half its rate, so the high frequencies are gone before they can fold. Some plug-ins build this in as a pre-filter you can switch on.
The clean versions of both
Each effect is the crude form of something your DAW does carefully every day. Lowering bit depth is what happens when you export a 24-bit session as a 16-bit WAV. Done properly, it adds dither first, a very quiet noise that stops the rounding error following the music, so it comes out as a faint, even hiss more than 90 dB below full scale instead of grain. A bitcrusher skips the dither and uses far fewer bits so the error stays audible.
Lowering the sample rate is what happens when a 48 kHz file is converted to 44.1 kHz. Proper conversion filters out everything above the new limit, then calculates new samples on a smooth curve, so nothing folds and nothing steps. A downsampler skips both steps on purpose, although the lab's Anti-alias switch adds the first one back in front of it.
The sample rate and bit depth lesson covers choosing the clean settings for a project, and aliasing and oversampling explains how other effects avoid folding.
Using a bitcrusher and a downsampler together
Early samplers cut both numbers to save memory, which is why records made on them have a bit of each. A second of 16-bit audio at 44.1 kHz takes 705,600 bits per channel. The E-mu SP-1200 sampled at 12 bits and 26.04 kHz, which comes to 312,480, less than half. Halving either number halves the data, but the cost is different: going from 16 to 8 bits loses about 48 dB of clean range, while going from 44.1 to 22.05 kHz loses the top octave, everything from about 11 to 22 kHz.
When the two sit next to each other, the order doesn't change anything. Rounding a held sample gives the same number as holding a rounded one, so a crusher into a downsampler sounds exactly like a downsampler into a crusher. Order matters once something sits between them or around them, like a filter, a drive stage or a reverb.
The lab's third card runs both in series, set here to the SP-1200 numbers, so you can hear the combination before setting it up in your DAW:
To set it up in your DAW:
- Set the rate firstStart the downsampler at 22 kHz and bring it down until the top end goes dusty. Between 12 and 26 kHz sounds like an old sampler, and under 8 kHz it starts to sound like a phone or a toy.
- Get the level right going inMake sure the sound peaks close to 0 dBFS when it reaches the bitcrusher, with a gain plug-in in front if it needs one, so it has every level to use.
- Add the grainBring the bits down from 16 until you can hear grain on the tails. 12 bits is subtle and 8 is plain; at 6 or fewer, everything turns gritty.
- Filter around itIf melodic parts clash with the key, put a low-pass filter before the downsampler at about half its rate. If the result is too fizzy, put another after the bitcrusher.
- Compare at the same loudnessSwitch it off and on with the levels matched, and listen in the full mix as well as soloed.
Which one to use
| Job | Bitcrusher | Downsampler |
|---|---|---|
| Old-sampler drums | 12 bits for grain | 12 to 26 kHz, the main ingredient |
| Grit on a snare or drum bus | 4 to 8 bits, blended in | Roughens cymbals more than the hits |
| Phone or radio voice | Breaks up word endings | 6 to 8 kHz, with a high-pass at 300 Hz |
| Edge on a bass line | On a high-passed copy | Mostly leaves the notes alone |
| Chiptune or robotic lead | Adds grit that stays in key | 4 to 8 kHz for the metallic ring |
| Pads, keys and long tails | Cuts the tails short | Dulls them but keeps them whole |
On quiet parts and long tails, the downsampler is the safer choice, because it leaves their level alone. On a loud melodic part such as a lead or a bass line, pick the bitcrusher, because its harmonics follow the notes. The bitcrushing and sample rate reduction lessons have starting settings for each effect on its own, and the saturation lesson puts both next to tape, valve and clipping.
Common mistakes
Turning the wrong knob
If you want a duller, older top end, turning the bits down won't get you there. Bit depth never lowers the frequency limit; it adds grain and leaves the top where it was. The rate knob is the one that dulls it.
Crushing a quiet sound
A bitcrusher treats a sound peaking at −18 dBFS as if it had three fewer bits than one peaking at 0 dBFS. If a part turns to noise and cuts out, turn it up ahead of the crusher before you blame the setting.
Trying to EQ out the aliasing
Folded tones from a downsampler sit right among the music. Cutting them cuts the part too, so raise the rate or filter before the downsampler.
Comparing them at different levels
Both effects add energy up top, so either one can seem louder and more exciting than the clean sound. Match the loudness before you decide which one you like, which is what the lab's Auto gain does.
Train your ears
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 loudness matched, and asks which one it was. Listen to the quiet ends of notes, which the bitcrusher turns to grain, and to the top end, which the downsampler replaces with a metallic ring. Try it on the chords first, then on the vocal.
Questions people ask
Which one gives the lo-fi sampler sound?
Mostly the sample rate. The dull, slightly metallic top end of old samplers comes from a low rate, and the bit depth adds grain on top. A downsampler at 26 kHz with a bitcrusher at 12 bits matches the numbers of the E-mu SP-1200, though its converters and filters added to its sound as well.
Does the order of a bitcrusher and a downsampler matter?
Not if they're next to each other with nothing in between. Rounding a held sample gives the same number as holding a rounded one, so the output is identical. The order starts to matter once there's a filter, a drive control or another effect between them.
Is 8-bit music made with an 8-bit bitcrusher?
Not really. The 8 in 8-bit music refers to the processors in consoles like the NES. The sound comes mostly from the simple square, triangle and noise waveforms their sound chips played, so a bitcrusher on its own gets you only part of the way.
Why does a phone call sound cleaner than an 8-bit crusher?
Phone lines have traditionally used 8 kHz and 8 bits, but the bits are spaced unevenly, with fine steps near silence and coarse ones near full scale, so quiet speech keeps its detail. A bitcrusher spaces its steps evenly, which gives quiet sounds the coarsest treatment.
Does a bitcrusher plug-in lower the sample rate too?
Only if it has a rate, downsample or frequency control, and most do: Ableton Live's Redux and Logic Pro's Bitcrusher both have one alongside the bit depth control. Bits alone never change how often the samples are updated.
Which is better on drums?
They do different jobs there. The downsampler roughens the hi-hats and cymbals and gives the whole kit an old-sampler feel. The bitcrusher leaves the top end and adds grit and density to every hit, though it shortens the tails, so blend it in with the mix control.