Using the Delta 66 with your Software Application

Synchronization

For proper operation, the entire Delta 66 system is always synchronized to a single master clock. The master clock is chosen via the Delta Control Panel software and this clock may be derived from either the Delta 66’s internal crystal oscillators or S/PDIF In. Most of the time the master clock is taken from the internal crystal oscillators. However, the S/PDIF option is used in situations where the Delta 66 must be synchronized to external digital audio or sample rates.

As stated, most of the time the master clock is derived from the internal crystal oscillators. Operation in this mode is similar to that of a generic sound card — for instance, when a WAV file is played through the Delta drivers, the software application playing the WAV file is responsible for setting the sample rate in the sound card hardware. The Delta 66 supports these sample rates by using either of its internal crystal oscillators and dividing the rate of that oscillator by some value to derive the proper sample rate.

In situations where S/PDIF In is being used, the Delta 66 should be configured to get its master clock from the S/PDIF In data stream. The reason for this is simple — even if the sample rates are set the same, an S/PDIF data stream coming from an external source is rarely going to be in sync with the Delta 66 (or other digital audio devices in the system for that matter). If the master clock were set to use the internal crystal, then the incoming S/PDIF audio would have “pops,” “crackles,” and other undesirable audio artifacts present in it. Instead, setting the master clock to “S/PDIF In” will synchronize the Delta 66 to the S/PDIF input data and its digital audio will be transferred properly.

Finally, the S/PDIF In option may be used to operate the Delta 66 at non-standard sample rates. When this option is selected, the Delta 66’s sample rate will automatically match that of the incoming S/PDIF data stream.

NOTE: When the S/PDIF In is selected as the master clock source, the Delta 66 mixer’s frequency response will be affected by whatever sample rates you inject at the S/PDIF In. This is because (1) the digital mixer operates at the same sample rate as the rest of the board, and (2) sample rate and frequency response are directly correlated.