Chapter 8: TL MasterMeter
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1948, when a waveform has all frequencies re-
moved above the Nyquist frequency, the result-
ing waveform will be the original waveform that
was sampled.
This process is significantly more involved than
simply “connecting the dots” between sample
points. Today it involves extremely sophisti-
cated means of reconstructing the waveform,
using filters that are highly complex mathemat-
ical systems utilizing “oversampling,” “upsam-
pling,” “linear phase, equiripple FIR” designs
and much more.
Oversampling creates a more accurate digital
representation of an analog signal by sampling
some number of times per second (frequency)
and converting into digital form. Oversampling
requires at least twice the bandwidth of the fre-
quency being sampled. For example, a con-
sumer CD player using 2x oversampling is pro-
cessing information at 88.2 kHz.
The result is that today’s digital to analog con-
verters get closer to the original than ever be-
fore, making music played on systems today as
accurate as possible. Even today’s inexpensive
components such as off-the-shelf CD players
have drastically improved filters and thus better
reconstruction abilities than in years past.
Application
Most contemporary audio recording is done
with Digital Audio Workstations (DAWs), al-
though digital mixing systems in the form of
outboard digital mixers are also very popular. To
the user, these digital systems appear similar to
traditional audio tools and are designed order to
emulate the operation of a conventional analog
recording system.
One familiar analog tool that has been carried
over to the digital realm is a “peak meter” that
tells the amplitude of the waveform’s peaks. In
the analog realm, peak signal was an indicator
that would alert the audio engineer when the
peak signal level was getting too high. A peak
signal in analog recording would cause the tape
to saturate, creating distortion. In an analog sys-
tem however, this type of distortion was often
deliberately engineered into tracks in order to
achieve a certain sound.
In the digital realm this type of meter is impor-
tant and more vital, because if the amplitude of
a waveform exceeds the top of the measurable
scale (full scale, or “full code”), the signal will
“clip” causing unwanted and unpleasant distor-
tion rather than the traditional distorted sound
of analog. This digital clipping occurs because
the waveform is “lopped off” and the data is
changed. When the waveform is reconstructed
it cannot be accurately done in order to repre-
sent the original waveform. Instead, it has a sig-
nificant amount of inharmonic distortion
caused by aliasing. For this reason, digital re-
cording has a maximum level at which signals
can be recorded. Anything exceeding this level
(full scale) has undesirable consequences.
The method used for computing the peak value
inside the system however is not particularly ac-
curate. DAW systems typically take the ampli-
tude of the samples and use these as the basis for
the peak meter. The problem with this approach
is easily identified: the samples themselves do
not represent the peak value of the waveform.
The waveform is only complete after the recon-
struction process. Until this process has been
completed, the waveform is inaccurately repre-
sented by the samples. This is the reason that in
most DAWs the waveform is represented on the
screen as a “dot to dot” connection between
sample points. They do not undergo the recon-
struction process inside the system, so all that