Alesis Hammerfall DSP System manual Recording a Subgroup Loopback, Recording a Softwares playback

26.5 Recording a Subgroup (Loopback)

The HDSP series uses TotalMix also for a routings of the subgroup outputs (=hardware outputs, bottom row) to the recording software. Unfortunately this feature is not available with the HDSP MADI, as the FPGA of the card has no resources left. Therefore this chapter describes the loopback mode when used with an external cable loop. As the HDSP MADI has only one input, an external cable loop will only make sense for the following examples in case the signal had been split up into several wires. This can be done easily when using the ADI-648, splitting the MADI line into eight 8-channel ADAT lines. Then a loopback of specific channels is possible.

A loopback is used to record the playback signal. This way, complete submixes can be re- corded, the playback of a software can be recorded by another software, and several input sig- nals can be mixed into one record channel. Please note these important issues:

The connection of digital output and input generates a clock loop, and with this a malfunc- tion, in case the card has not been switched into clock mode Master, or an external clock signal of highest priority is used.

The latter is the case when the card is in AutoSync mode, and is synchronized by an external clock signal from the input selected in Pref Sync Ref.

Connecting digital output and input can cause a digital feedback, which is more severe than any analog one. Caution!

This is a problem for both TotalMix (monitoring an input signal to the same output channel) and the DAW software (which usually activates monitoring in the same way).

Recording a Software's playback

In real world application, recording a software's output with another software will show the fol- lowing problem: The record software tries to open the same playback channel as the playback software (already active), or the playback one has already opened the input channel which should be used by the record software.

This problem can easily be solved. First make sure that all rules for proper multi-client operation are met (not using the same record/playback channels in both programs). Then route the play- back signal via TotalMix to a hardware output in the range of the record software, and send it to the record software via the loopback cable.

Mixing several input signals into one record channel

In some cases it is useful to record several sources in only one track. For example when using two microphones when recording instruments and loudspeakers. TotalMix loopback saves an external mixing desk. Simply route/mix the input signals all to the same output (third row), then send this output to a record channel via the loopback cable. This way any number of input channels from different sources can be recorded into one single track.

Note: The data recorded via loopback is delayed by about 3 samples, when using an additional ADI-648 by about 6 samples. This value is extremely low, because the HDSP 9652 provides digital interfacing only. And therefore the additional delay can simply be ignored.

User's Guide HDSP MADI © RME 59