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Duplex Delay Dialog
This dialog summarizes the Duplex Delay and Drift values determined via Auto-Calibration, and also allows you to make temporary or permanent manual changes to the Delay values. You can activate this dialog from the Calibration menu via ALT+C, D, or directly via CTRL+SHIFT+D.
Duplex Delay is the difference between an input sample number and the corresponding output sample number, since Windows and the sound card treat input and output as two separate processes that are not necessarily synchronized. Drift is the change in Delay over a fixed interval.
If Delay is constant, then Daqarta corrects for it automatically. Otherwise (non-zero Drift) the input and output can't maintain alignment. On many sound cards, this happens when using sample rates that are not integer sub-multiples of 48000 Hz. Even the CD standard of 44100 Hz may exhibit drift on these cards.
Delay and Drift values are shown for up to 4 different sample rates. The labels start out as 'Rate 0' through 'Rate 3', but change to the actual rates used during up to 4 Auto-Calibration runs.
Values are shown for all combinations of 1 and 2 outputs and inputs. If a value has not been determined yet, it is shown as '****'.
While you are running in one of these full-duplex modes, the current Delay setting is shown in the Manual Delay control. If the mode is uncalibrated, the default Delay value is the last calibrated mode used in the current session, or zero if no calibrated mode has been used yet.
You can change the current delay directly with this control. Values in the range of +/-4096 samples are accepted. The value you enter is temporary unless you hit Set, in which case it will update the proper entry in the summary and be retained for future sessions.
Note that if the current sample rate is not one of those already listed, hitting Set will cause the current rate to be included in the list, replacing the last rate if needed. All values will be shown as uncalibrated ('****') except for the one you just set, which will appear in the column for the current channel configuration.
The proper value for Delay can be determined via a loopback from output to input. If Delay is correct, the input and output waveforms should be perfectly aligned in time. (They may have different amplitudes, so they may not overlap exactly.) However, note that when the signal is a repeating waveform, it's possible to have a situation where the signals appear to align, but they are really off by an integer number of waveform cycles. It's best to use an infrequent pulse or tone burst to be sure.
Auto-Calibration (with Duplex Delay checked) uses a pulse which is high for 16 samples, then low for 16 samples, repeated at a 5 Hz rate. You can use this same test waveform for your manual tests by loading AutoCal.GEN and toggling off Stream 0 (Sine) and toggling on Stream 1 (Pulse) for the Left output.
NOTE: The Duplex Delay dialog is not available after the trial period, unless a paid license key is present.
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