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Perserve your bits! (Mixing
& Mastering)

Studio Overviews

Posted by CapnZilog - Feb 25, 2003
@ 04:03:08 AM

CD's may be 16-bit, but your
masters shouldn't be - and here's why

Here's a little background on how
I mastered a recent song, after a friend of mine asked me what
seemed a simple question: Why isn't mixing down to 16-bit good
enough? Particularly when the tracks were recorded in 16-bit
and CD's are still 16 bit?

Even though the tracks in
most of my recordings are recorded at 16-bit, 44.1KHz, I still
mix down to 24-bit unless I know I'm never, ever going to
master the final mix outside of SONAR.

Mixing is
additive. Say you have EIGHT 16-bit tracks playing at the same
time, and they're all at maximum amplitude.

How can
this result fit within 16 bits? It can't, so you end up
reducing the output bus gain until the mix no longer clips.
When this happens, precision (bits) are lost. How many bits?
In this case, three. Each doubling of tracks adds one bit to
the final result.

Here's the math: (I'm doing this
unsigned, to simplify things)

Max value in a 16-bit
sample : 65536 * 1 = 65536   = 2^16 (i.e., 16
bits)

Max value when mixing 2  16-bit samples :
65536 * 2 = 131072  = 2^17 (17 bits)
Max value when
mixing 4  16-bit samples : 65536 * 4 = 262144  =
2^18 (18 bits)
Max value when mixing 8  16-bit samples
: 65536 * 8 = 524288  = 2^19 (19 bits)
Max value when
mixing 16 16-bit samples : 65536 * 8 = 1048576 = 2^20 (20
bits)

Hence, every doubling of tracks, if added
together worst-case, would require a D/A converter with one
additional bit of precision to avoid overflow. If you were
mixing together SIXTEEN 16-bit tracks to CD mix for CD, you'd
need 20 bits just to audition the result! Since you don't have
it, so you end up lowering the stereo mix bus by ~24dB just to
avoid clipping. And when this happens, you're effectively
THROWING AWAY 4 bits of audio quality.

When mixing down
to 16-bit in SONAR, the "lost bits" can be preserved after a
fashion using dither. Dither is a low-level noise added to the
mix that gives a small mathematical nudge to bits that would
otherwise be lost when converting to a lower precision such as
16-bit.

What happens is that the human ear averages
this noise out in such a way that it SOUNDS as if some of the
lost bits are still present. There's no free lunch, but the
perceived increase in audio quality (particularly for very
quiet signals) more than makes up for the small amount of
additional hiss. If you absolutely, positively will not be
performing mastering upon your final mix, this is a good
method.

=HOWEVER!= (and this is the payoff for reading
this far)

It's best to ALSO mix down your tracks to the
highest precision that SONAR will allow (that's 24-bits) and
archive that file somewhere. When you get SIGNED to a LABEL
and it's time to send your stuff off for MASTERING, give them
the 24-bit mix and let them handle not only the tweaks (EQ,
compression, etc) but also the 24 to 16-bit conversion process
for CD.

Signal processing almost always involves some
kind of loss. Whether you're changing the volume, EQing a
signal, recompressing a section or whatever, bits are being
lost due to rounding error. And that's why you want to perform
all these kinds of mastering techniques on the highest quality
mix, secure in the knowledge that at least it's not going to
sound WORSE than 16-bit by the time you're done.

So,
burn a 16-bit mix to CD whenever you like - but always keep
that 24-bit mix lying around because now matter how good that
CD is, it's never going to be as good as your original
master.

Recommended
Reading:
http://www.izotope.com/products/audio/ozone/ozoneguide.html

-Cap'n
Zilog, DSP engineer

11 comment(s) | viewed 430
time(s) | |

Your Comments

Commented by Zero - Feb 26, 2003 @ 12:55:23
AM

hmmm if i had a buck for every way
that confused me, i could buy 10 happy meals :)

ok ok
just kidding i understood most of it, i've heard alot of talk
about bits and compression and all that whodada, this is why i
now only ever increase volume, recording at -6 helped soooooo
much and i hardly ever EQ it's all done on the external zoom
mrs-1044, i like to get the sound eq'ed jsut right, before i
record the track :)

Commented by CapnZilog - Feb 26, 2003 @
01:47:09 AM

These are admittedly pro-level
concerns; in fact, you may not even be able to hear the
difference in quality by the time you've run your mix through
a lossy codec like MP3. However, if you hate the idea of
degrading your mixes AT ALL then it's important to grasp this
stuff.

If you're a star though, don't worry - Bob
Clearmountain will take care of it.

Commented by guitwiz - Mar 01, 2003 @ 01:35:17
PM

WOW!!!!!!!

Commented by Xenophage - Mar 13, 2003 @
11:49:38 PM

Capn, this made absolute
sense.  Thanks a TON for the info!

Commented by CapnZilog - Mar 17, 2003 @
05:00:28 PM

You're very welcome. A few weeks
after I wrote this, a very similar article came out in MIX but
the math is hosed. If you're using SONAR, the ability to
export to 24-bit with dither is a very good reason to use
"Export Audio" to create your mixes as opposed to just
bouncing everything down to two tracks.

I've been
badgering my former Cakewalkers to support 32-bit FFP as a
native mixdown/file format for some time. I just heard last
week from the horse's mouth that we should expect this feature
in SONAR 3, yeah baby!

Commented by MAJICHANDS - Jul 18, 2003 @
04:43:42 AM

Cap, not to get too off topic, but
can you seriously hear a difference between 16/44 and 24/48?
To be honest, I can't and I like to think my ears are pretty
well conditioned and not burned out since I never do anything
at extreme volumes. Now when I use 24/96, I can tell a huge
difference, but 24/48 sounds as good as 16/44 to my ears. Are
my ears messed up? What difference should I hear between the
2, and how noticable is it? Thanks....good
artical.

Danny

Commented by CapnZilog - Aug 07, 2003 @
03:25:21 AM

It's like taking a photocopy of a
photocopy; you try to avoid it if you can. Now, for our BIG
COMPRESSED ROCK tracks, you might not be able to hear the
difference between a CD mix and a DVD Super-Audio mix except
in the fadeouts.

Jazz and classical purists are much
more concerned over the issue, and I'll say right now that I
believe word length, A/D D/A accuracy & jitter to be more
important than dog-whistle sampling rates in the real
world.

Commented by MAJICHANDS - Aug 07, 2003 @
05:54:47 PM

Ah thank you Cap...was great to
talk to you last night man. You're a walking book of
information, and an asset to the site. I'm just glad (after
our conversation on this last night) that I'm not crazy for
not hearing a major difference in those sample rates!
:)

Commented by String Devil - Feb 06, 2006 @
06:25:51 AM

thanks cap.. just read the article
3 years later LOL! :)

Commented by VanHelsing - Feb 10, 2006 @
03:22:15 AM

Me too!!! ;)

Commented by CapnZilog - Feb 15, 2006 @
04:41:22 AM

(3 years later)

Y'know, we
did ultimately get 32-bit mixdown support in SONAR... but it
didn't happen until SONAR 5!!

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