Master Clock - TerraTec EWS88 MT Manual

Master Clock.

This section is all about the sampling rate, which is being used to drive the EWS88. This is an
important point, as the card can be synchronized to an external signal (i.e. a DAT-recorder) or
internally (Internal) and pass the clock signal on to other devices. If there is a valid digital
signal connected to the digital-in connectors (S/PDIF or ADAT) its sample rate will be displayed
in the EWS ControlPanel and the EWS will be switch to external syncing. In addition, any card
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defined as a "Slave", and connected to other EWS cards with the EWS -Connect connection
will also be switched to external (see page 45). In Master/Slave mode , all "Slave" cards
cannot be switched back to internal clocking, as the clock is provided by the "Master" card.
The "Master" card can of course be clocked internally, and externally via a digital input.
Example: The EWS88 D is clocked by the EWS88 MT in Master/Slave mode, which, in turn, is
switched to external synchronization via its digital S/PDIF input, connected to a Minidisk
player. As the Minidisk player is running at a sampling frequency of 44.1kHz, the entire EWS
system is switched to 44.1kHz and everything runs in perfect sync.
Now it becomes interesting: The DSP of the AudioSystem EWS88 is not equipped with a
sample rate converter (only exception: the SystemSound driver, more of which on page 50).
This building-block, which is very common in today's sound cards ensures, that you can
playback and listen to signals with different sampling rates. It achieves this by "inter-locking"
frequencies. For example: Your card is clocked to a DAT-recorder with 48kHz (externally).
Then, you are working on a file, using your 44.1kHz Wave editor. While you are playing your
file, Windows plays a SystemSound (22.05 kHz) while a text-message pops up. All sample
rates are audible simultaneously, in 48 kHz – the externally synced sampling rate. Everything
appears to be normal, even though audio files are not played using their respective sampling
frequencies. If you listen carefully, though, you will notice a difference in sound quality. You
see, the quality suffers when using this fundamentally useful converter – no matter how good
it is. As the AudioSystem EWS88 is not a conventional sound card, and you would not be at all
happy, if you found out that half of your songs had been recorded using the wrong sample
frequency, we have chosen not to implement a sample rate converter. Instead, the sampling
rate is adjusted dynamically to the required sampling frequency. Without any loss in sound-
quality, of course. Just as it should be with a quality recording. But: If you try to play different
audio-files with different sampling-frequencies, you will receive an error-message. Though it is
possible to playback different audio files from different programs, they need to have the same
sampling frequency. In addition, you need to ensure that the "Wave Playback/Record Mode"
is set to "Multi-Application". More on this is to follow.
The button "Rate Locked"allows you to lock the sampling-frequency to a value (externally
set). This way, you will avoid recording different sampling frequencies by accident. For
example: A production is to be recorded exclusively in 96kHz. If you lock the sampling-
frequency to 96kHz, no audio-file with a different frequency will be able to "sneak in". You will
be notified.
AudioSystem EWS88 57