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Dithering
Gazillion Industries ·
The last checkbox in the export dialog, the one nobody understands, sitting
there asking whether you want to add noise to a record you just spent a week cleaning up. The
answer is usually yes, and the reason is a genuinely strange piece of engineering.
Dither is a tiny amount of noise added deliberately before you reduce bit depth, because the
errors caused by that reduction are worse than the noise. Truncating a 24-bit file to 16-bit
produces rounding errors that follow the signal, which the ear hears as distortion on quiet
material. Adding noise first makes those errors random instead, turning a correlated distortion
into an unobtrusive hiss. Apply it once, at the very end, only when you are actually reducing bit
depth.
The short version
- What
- noise added before reducing bit depth
- Why
- it converts rounding distortion into steady noise
- When
- only when going to a lower bit depth, usually 16-bit
- Where
- last, after the limiter, once and only once
- Type
- triangular is the standard safe choice
- Noise shaping
- moves the noise to where the ear cares less
Why rounding is worse than noise
A 24-bit sample has far more possible values than a 16-bit one. When you convert, every value
has to move to the nearest available step, and the amount it moves is the error. That error is
not random: it depends on the signal, so it tracks the music, and anything that tracks the music
is heard as distortion rather than as background.
On a loud passage the error is minuscule compared to the signal and nobody will ever hear it.
On a fade-out, a solo piano note decaying into silence, or a quiet ambient passage, it is
audible as a grainy, gritty edge that gets worse as the music gets quieter, which is exactly
backwards from how noise behaves.
Dither breaks the correlation. Add a small amount of random noise before the conversion and
the errors stop following the signal, because the thing being rounded is now signal plus noise.
You trade a distortion that appears when the music is quiet for a constant noise floor a few
decibels above where it would otherwise be. In every listening test that matters, that is the
better trade.
Types, briefly
- Triangular (TPDF) is the standard choice and the one to use if you do not
want to think about it. It fully decorrelates the error at the cost of a slightly higher noise
floor.
- Noise shaping adds the same total amount of noise but moves most of it
into frequency ranges the ear is less sensitive to, usually the top octave. It measures worse
and sounds better.
- Aggressive noise shaping pushes that further. On material destined for
further processing it is a bad idea, because that shaped noise is now baked in.
BEEFY lives
much earlier in the chain than this: saturation and loudness, with SOFT CLIP holding the peaks
long before anything gets exported.
The rules
- Dither only when reducing bit depth. Exporting 24-bit from a 24-bit session needs
none.
- Dither once, on the final export. Dithering a file that was already dithered adds noise
without benefit.
- Put it last, after the limiter. Anything after dither re-quantizes and undoes the
point.
- If you are delivering 24-bit masters to a distributor, let them dither when they encode.
Do not do it for them.
- Triangular unless you have a reason. The reason is usually quiet classical or acoustic
material, where noise shaping earns its keep.
Where it costs you
Honestly: on a loud modern master, very little either way. The noise floor of a 16-bit file is
low enough that the difference between dithered and truncated is inaudible under a record that
never drops below a moderate level. The people who genuinely need this are working on material
with real quiet passages. Everyone else should do it because it is free and correct, not because
they will hear it.
The real cost is double-dithering and dithering at the wrong stage, both of which add noise
for no reason.
Questions people ask
Should dithering be on or off?
On, if the export is reducing bit depth, usually to 16-bit. Off if you are exporting at the
same bit depth you worked at, or handing a 24-bit file to someone who will process it
further.
Does dither lower quality?
It raises the noise floor very slightly and removes a distortion that would otherwise appear
on quiet material. By any measure that matters musically, it improves the result.
Should I add dither to my master?
If the master is being delivered as a 16-bit file, yes, on the final export only. If you are
delivering 24-bit, no.
What does dithering mean in music?
Adding low-level noise before a bit-depth reduction so that the rounding errors become random
noise rather than signal-dependent distortion.
What BEEFY does
BEEFY is our saturation and loudness effect, and the reason it appears in an article about
dither is the shape of the chain. BEEF, COOK and
JUICE do their work on the source or the bus; SOFT CLIP opens
switched on and rounds the loudest parts so the peaks are dealt with early;
LIMIT holds the output when you want that instead. Dither is the very last thing
that happens, after all of it, in the export dialog.
Add noise on purpose, at the end, to make the quiet parts sound cleaner. Engineering is not
always intuitive.
Keep reading
- True peak — Why a file can read zero and still clip, and what ceiling to use.
- Headroom in mixing — How much to leave, and why the usual explanation is out of date.
- How to master a beat — Headroom, a plain chain, clipping before the limiter, and the checks.
BEEFY — saturation and loudness plugin for Mac and Windows. There is
a 28-second demo with three without/with comparisons on the page.
Hear it — $19