EC-2 96kHz A/D/D/A upgrade
• appendix A
A-8
EC-2 Manual
About the EC-2’s audio
performance
An HD24 with the EC-2 upgrade has audio
performance far superior to that of any analog
recorder, and a wider dynamic range than most
input and output devices that may be connected to
it. Here’s why:
The converter defines the sound
The first and last steps in digital recording—the
conversion from analog to digital, then back
again—define the audio quality of the digital
recording process. Once captured in the digital
domain as a series of ones and zeroes, the audio is
protected for as long as the media lasts. So the
converter you use when recording a master is one of
the most important choices you can make in the
studio.
The EC-2 upgrade uses premium AKM 5393
analog-
to-digital (A/D) and AKM 4393 digital-to-analog
(D/A) converters, among the best available today.
The input and output electronics are virtually
identical to those of the acclaimed Alesis
MasterLink High-Resolution Master Disk Recorder.
Even at standard sample rates, the noise floor and
distortion are lower than most units costing much
more. The noise floor is 10 dB lower than a “stock”
HD24, and 20 dB lower than standard Compact
Discs and the original 16-bit ADAT. How much is
10 dB? From a laboratory standpoint, 20 dB stands
for 100 times the power—so the dynamic range
increase is analogous to the difference between a 10-
watt amplifier and a 1000-watt amplifier. Because
of the logarithmic nature of human hearing, to most
people, each -10 dB of difference sounds “half as
loud”, so the noise floor of the EC-2 will be
perceived as 1/4
th
that of a standard CD.
The resulting 112 dB dynamic range is not only
more than that found on a standard Compact Disc,
it is much wider than the acoustic dynamic range of
even the best recording studios. When you record
analog audio directly into an ADAT HD24
upgraded with an EC-2, the recorder is literally no
longer an issue in the overall sound quality. Even
dedicated (and expensive!) outboard converters
connected to the ADAT Optical ports of the HD24
have a tough time beating the specs of the EC-2.
With proper recording techniques, any noise or hiss
you hear is coming from the self-noise of the
microphones or preamps, not from the HD24.
When to use 88.2/96 kHz
Why 44.1/48 kHz?
Many engineers believe that the sampling rates that
have been used up to now are less than ideal. The
industry-standard sample rates were chosen at a
time when digital storage was much more
expensive than it is today. The “consumer” rate of
44.1 kHz was the lowest possible sampling rate that
could still record and play back the highest
frequencies in the commonly-accepted human
hearing range of 20 Hz to 20,000 Hz. At a 44.1 kHz
sampling rate, a 650 MB Compact Disc would be
able to play back 72 minutes without
interruption—the length of Beethoven’s Ninth
Symphony.
In an era before digital mixing consoles and
computer workstations, the 48 kHz sampling rate
was designated the “professional” rate for two
reasons:
1. the slightly higher sampling rate allowed
more room for the
antialiasing filter
to do its
work, and
2.
professional recorders needed to be able to
“pitch down” 12% and still play back the full
20 kHz frequency range.
The case for a higher sampling rate
While the traditional sampling rates give excellent
performance (especially with today’s converter
technology), there is criticism that these rates are too
low to obtain truly audiophile quality. Most of this
criticism centers on the filters that are necessary to
make digital audio work.
Antialiasing filters
The Nyquist theorem, upon which digital audio
recording is based, states that you can reliably
record and play back any signal by sampling it at
least two times the rate of the highest frequency you
want to record. However, if there are any analog
frequencies in the incoming signal that are higher
than half the sampling rate, nasty-sounding
reflections appear in the signal, known as
aliases
.
For example, if a 47 kHz tone is sampled at 48 kHz,
you’ll hear a 1 kHz tone, right in the midband of the
audio—hardly what you’d want to hear by getting
“extended frequency response”.
So, early analog-to-digital converters had a steep
“brick wall” analog filter on the input. To avoid
