B Digital Audio Synchronization; C Sample Rate Conversion - Alesis AI-1 Reference Manual

leaving the digital domain. The AI-1 can be used to transfer digital
audio back and forth between DAT machines, CD player/ recorders
and digital audio workstations. Whenever you transfer digital audio
through the AI-1, the result is a perfect, exact duplicate of the
original with no degradation or change in audio quality.

1.2B Digital Audio Synchronization

All digital audio protocols, whether Alesis' Proprietary
Multichannel Optical Digital Interface or AES/EBU format, transmit
data plus a timing clock that dictates the speed at which the data
will be recorded or played back. This timing clock is related to the
sample rate. The ADAT speed is controlled automatically to
conform to this sample rate whenever its DIGITAL IN LED is lit.
Therefore, the PITCH controls on the ADAT have no effect when
performing digital transfers onto ADAT.

1.2C Sample Rate Conversion

The AI-1 also provides conversion between 48kHz and 44.1kHz
sampling rates. If you are recording onto ADAT from a source that
is running at 44.1kHz, you can either record at the same rate, or
convert it to ADAT's superior 48kHz sampling rate. One of the best
ways to use ADAT is not only as a multitrack recorder, but as a
mixdown recorder as well, using two tracks to mix to. Using the AI-
1, you can transfer the two-track mix to DAT or a CD recorder and
simultaneously convert the audio to the required 44.1kHz sample
rate.
Because of its superior sound quality, it is always better to record
onto ADAT at the 48kHz rate, even when the original audio was
recorded at 44.1kHz. Contrary to what many people think,
converting 44.1kHz audio to 48kHz does not change the sound
quality in any way. If, however, you choose to not to convert such
an audio source and record it onto ADAT at 44.1kHz, don't be
surprised when you play back the ADAT recording and hear the
music a little faster and transposed up a bit. This is because 48kHz is
literally a faster sampling rate than 44.1kHz. When the AI-1 sends
44.1kHz audio to ADAT, the ADAT's motor slows down to match
the rate of the incoming audio. If you are monitoring other pre-
recorded tracks on the same machine, you'll notice that they are
now slower and transposed down.
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