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28.5 Recording a Subgroup (Loopback)<br />
TotalMix supports a routing of the subgroup outputs (=hardware outputs, bottom row) to the<br />
recording software. Unfortunately this feature is not available with the H<strong>DSP</strong> <strong>9652</strong>, as the<br />
FPGA of the card has no resources left for a hardware implementation. Therefore this chapter<br />
describes the loopback mode when used with an external cable loop.<br />
A loopback is used to record the playback signal. This way, complete submixes can be recorded,<br />
the playback of a software can be recorded by another software, and several input<br />
signals can be mixed into one record channel. Please note these important issues:<br />
60<br />
The connection of digital output and input generates a clock loop, and with this a malfunction,<br />
in case the card has not been switched into clock mode Master, or an external clock<br />
signal of highest priority is used.<br />
The latter is the case when the card is in AutoSync mode, and is synchronized by an external<br />
clock signal from the input selected in Pref Sync Ref. For example set up a loopback cabling<br />
with SPDIF or ADAT3, but clock the H<strong>DSP</strong> <strong>9652</strong> via input ADAT1.<br />
Connecting digital output and input can cause a digital feedback, which is more severe<br />
than any analog one. Caution!<br />
This is a problem for both TotalMix (monitoring an input signal to the same output channel) and<br />
the DAW software (which usually activates monitoring in the same way).<br />
Recording a Software's playback<br />
In real world application, recording a software's output with another software will show the following<br />
problem: The record software tries to open the same playback channel as the playback<br />
software (already active), or the playback one has already opened the input channel which<br />
should be used by the record software.<br />
This problem can easily be solved. First make sure that all rules for proper multi-client operation<br />
are met (not using the same record/playback channels in both programs). Then route the<br />
playback signal via TotalMix to a hardware output in the range of the record software, and send<br />
it to the record software via the loopback cable.<br />
Mixing several input signals into one record channel<br />
In some cases it is useful to record several sources in only one track. For example when using<br />
two microphones when recording instruments and loudspeakers. TotalMix loopback saves an<br />
external mixing desk. Simply route/mix the input signals all to the same output (third row), then<br />
send this output to a record channel via the loopback cable. This way any number of input<br />
channels from different sources can be recorded into one single track.<br />
Note: The data recorded using the loopback cable are delayed by about 3 samples. This value<br />
is extremely low, because the H<strong>DSP</strong> <strong>9652</strong> provides digital interfacing only. And therefore the<br />
additional delay can simply be ignored.<br />
User's Guide H<strong>DSP</strong> <strong>System</strong> H<strong>DSP</strong> <strong>9652</strong> © <strong>RME</strong>
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