Re: [LAU] normalize from command line

Here's a copy of a very good article about normalization, it's from
http://www.hometracked.com/2008/04/20/10-myths-about-normalization/

10 Myths About Normalization

Sunday, April 20th, 2008 in Articles for Beginners by des

distortionThe process of normalization often confuses newcomers to
digital audio production. The word itself, “normalize,” has various
meanings, and this certainly contributes to the confusion. However,
beginners and experts alike are also tripped up by the myths and
misinformation that abound on the topic.

I address the 10 most common myths, and the truth behind each, below.
Peak Normalization

First, some background: While “normalize” can mean several things (see
below), the myths below primarily involve peak normalization.

Peak normalization is an automated process that changes the level of
each sample in a digital audio signal by the same amount, such that the
loudest sample reaches a specified level. Traditionally, the process is
used to ensure that the signal peaks at 0dBfs, the loudest level allowed
in a digital system.

Normalizing is indistinguishable from moving a volume knob or fader. The
entire signal changes by the same fixed amount, up or down, as required.
But the process is automated: The digital audio system scans the entire
signal to find the loudest peak, then adjusts each sample accordingly.

Some of the myths below reflect nothing more than a misunderstanding of
this process. As usual with common misconceptions, though, some of the
myths also stem from a more fundamental misunderstanding – in this case,
about sound, mixing, and digital audio.
Myths and misinformation

Myth #1: Normalizing makes each track the same volume
Normalizing a set of tracks to a common level ensures only that the
loudest peak in each track is the same. However, our perception of
loudness depends on many factors, including sound intensity, duration,
and frequency. While the peak signal level is important, it has no
consistent relationship to the overall loudness of a track – think of
the cannon blasts in the 1812 Overture.

Myth #2: Normalizing makes a track as loud as it can be
Consider these two mp3 files, each normalized to -3dB:
 [download MP3]

 [download MP3]

The second is, by any subjective standard, “louder” than the first. And
while the normalized level of the first file obviously depends on a
single peak, the snare drum hit at 0:04, this serves to better
illustrate the point: Our perception of loudness is largely unrelated to
the peaks in a track, and much more dependent on the average level
throughout the track.

Myth #3: Normalizing makes mixing easier
I suspect this myth stems from a desire to remove some mystery from the
mixing process. Especially for beginners, the challenge of learning to
mix can seem insurmountable, and the promise of a “trick” to simplify
the process is compelling.

In this case, unfortunately, there are no short cuts. A track’s level
pre-fader has no bearing on how that track will sit in a mix. With the
audio files above, for example, the guitar must come down in level at
least 12dB to mix properly with the drums.

Simply put, there is no “correct” track volume – let alone a correct
track peak level.

Myth #4: Normalizing increases (or decreases) the dynamic range
A normalized track can sound as though it has more punch. However, this
is an illusion dependent on our tendency to mistake “louder” for
“better.”

By definition, the dynamic range of a recording is the difference
between the loudest and softest parts. Peak normalization affects these
equally, and as such leaves the difference between them unchanged. You
can affect a recording’s dynamics with fader moves & volume automation,
or with processors like compressors and limiters. But a simple volume
change that moves everything up or down in level by the same amount
doesn’t alter the dynamic range.

Myth #5: Normalized tracks “use all the bits”
With the relationship between bit depth and dynamic range, each bit in a
digital audio sample represents 6dB of dynamic range. An 8-bit sample
can capture a maximum range of 48dB between silence and the loudest
sound, where a 16-bit sample can capture a 96dB range.

In a 16-bit system, a signal peaking at -36dBfs has a maximum dynamic
range of 60dB. So in effect, this signal doesn’t use the top 6 bits of
each sample*. The thinking goes, then, that by normalizing the signal
peak to 0dBfs, we “reclaim” those bits and make use of the full 96dB
dynamic range.

But as shown above, normalization doesn’t affect the dynamic range of a
recording. Normalizing may increase the range of sample values used, but
the actual dynamic range of the encoded audio doesn’t change. To the
extent it even makes sense to think of a signal in these terms*,
normalization only changes which bits are used to represent the signal.

*NOTE: This myth also rests on a fundamental misunderstanding of digital
audio, and perhaps binary numbering. Every sample in a digital (PCM)
audio stream uses all the bits, all the time. Some bits may be set to 0,
or “turned off,” but they still carry information.

Myth #6: Normalizing can’t hurt the audio, so why not just do it?
Best mixing practices dictate that you never apply processing “just
because.” But even setting that aside, there are at least 3 reasons NOT
to normalize:

   1. Normalizing raises the signal level, but also raises the noise
level. Louder tracks inevitably mean louder noise. You can turn the
level of a normalized track down to lower the noise, of course, but then
why normalize in the first place?
   2. Louder tracks leave less headroom before clipping occurs. Tracks
that peak near 0dBfs are more likely to clip when processed with EQ and
effects.
   3. Normalizing to near 0dbfs can introduce inter sample peaks.

Myth #7: One should always normalize
As mixing and recording engineers, “always” and “never” are the closest
we have to dirty words. Every mixing decision depends on the mix itself,
and since every mix is different, no single technique will be correct
100% of the time.

And so it goes with normalization. Normalizing has valid applications,
but you should decide on a track-by-track basis whether or not the
process is required.

Myth #8: Normalizing is a complete waste of time.
There are at least 2 instances when your DAW’s ‘normalize’ feature is a
great tool:

   1. When a track’s level is so low that you can’t use gain and volume
faders to make the track loud enough for your mix. This points to an
issue with the recording, and ideally you’d re-record the track at a
more appropriate level. But at times when that’s not possible,
normalizing can salvage an otherwise unusable take.
   2. When you explicitly need to set a track’s peak level without
regard to its perceived loudness. For example, when working with test
tones, white noise, and other non-musical content. You can set the peak
level manually – play through the track once, note the peak, and raise
the track’s level accordingly – but the normalize feature does the work
for you.

Myth #9: Normalizing ensures a track won’t clip
A single track normalized to 0dBfs won’t clip. However, that track may
be processed or filtered (e.g. an EQ boost,) causing it to clip. And if
the track is part of a mix that includes other tracks, all normalized to
0dB, it’s virtually guaranteed that the sum of all the tracks will
exceed the loudest peak in any single track. In other words, normalizing
only protects you against clipping in the simplest possible case.

Myth #10: Normalizing requires an extra dithering step
(Note: Please read Adam’s comment below for a great description of how I
oversimplified this myth.) This last myth is a little esoteric, but it
pops up sporadically in online recording discussions. Usually, in the
form of a claim, “it’s OK to normalize in 24 bits but not in 16 bits,
because …” followed by an explanation that betrays a misunderstanding of
digital audio.

Simply put: A digital system dithers when changing bit depth. (i.e.
Converting from 24-bits to 16-bits.) Normalizing operates independent of
bit depth, changing only the level of each sample. Since no bit-rate
conversion takes place, no dithering is required.
Other Definitions

Normalizing can mean a few other things. In the context of mastering an
album, engineers often normalize the album’s tracks to the same level.
This refers to the perceived level, though, as judged by the mastering
engineer, and bears no relationship to the peak level of each track.

Some systems (e.g. Sound Forge) also offer “RMS Normalization,” designed
to adjust a track based on its average, rather than peak, level. This
approach closer matches how we interpret loudness. However, as with peak
normalization, it ultimately still requires human judgment to confirm
that the change works as intended.

-- 
Speeding Cars - Imogen Heap (cover)
http://www.youtube.com/watch?v=SQ0_yUXidDI&feature=related
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