88.2/96 Khz Sampling Rates; The Tradeoffs; Ensuring Sample-Rate Compatibility - Alesis ADAT-HD24 Reference Manual

88.2/96 kHz sampling rates

The ADAT HD24 has the capability of recording at
twice the conventional sample rate. You can record
and play back at 88.2 kHz (double the consumer
rate of 44.1) or 96 kHz (double the professional
rate).
The HD24 can always record and play back high-
resolution signals via its ADAT Optical ports. But
its analog I/O, as shipped from the factory, is only
capable of operation up to 48 kHz. Your Alesis
dealer can install an optional upgrade kit that
allows analog input and output at the higher
sample rate (see page 66).
By recording at these high sample rates, frequency
response is doubled: instead of going to 20 kHz,
response is flat to beyond 40 kHz. But there are
some factors you should be aware of before
recording at these higher rates:

The tradeoffs

• At these higher rates, the HD24 becomes a
twelve-track (maximum) recorder, not 24-track.
• On a per-track minute basis, the available
recording time is cut in half since there are
twice as many samples being recorded to the
hard disk,
• Many other digital devices—notably most
digital mixing consoles and many computer
workstations—don't have 96 kHz capability, or
have compromised operation when they do
(less DSP, for example).
• Many sources in the studio such as most
microphones and almost all digital keyboards
have no response above 20 kHz that can be
recorded anyway.
• Most studio speakers aren't capable of
reproducing above 20 kHz, and when
presented with those higher frequencies the
speakers exhibit modes and resonances.
• Most experts believe that higher frequencies
above 20 kHz are not audible to the majority of
listeners.
However, formats such as DVD are capable of
bringing 24-bit, 96 kHz audio all the way to the
consumer, and to be able to have the best possible
ADAT HD24 Reference Manual
High resolution operation
masters in the future, a high sample rate may be
the way to go.

Ensuring sample-rate compatibility

Before you start recording a session at a high
sample rate you should plan your mixing and
mastering process so that you don't run into
problems later. Some of the questions you
should ask:
• If you are mixing digitally, does your digital
console support high sampling rates?
• Are you recording any digital sources such as
samplers or external A/D converters, and do
they support this sample rate?
• Does your mixdown device record at this
sampling rate?
• If you are taking the project to a mastering
facility after mixdown, can they process an
88.2 or 96k project?
• Finally, do you have the hard drive space to
record this project? Remember that 88.2 and
96kHz projects use twice as much drive space
per track as 44.1 and 48k projects.
88.2 kHz is a good choice if the tracks will be
mixed digitally to a Compact Disc format. The
sample rate conversion to convert this to the
44.1kHz rate used for Compact Discs is minimal
compared to the conversion required for 96kHz
recordings—you simply use every other sample.
chapter 7
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