Calibrating Universal Audio Interface--No Input Signal

[larrykohling]

Hello all,

I have been trying to calibrate my UAD Apollo 8p's sound card with REW. I am running Mac OS 12.2 Monterey. I have not been able to get an input signal.

The problem is, there seem to be no input or output volume controls available anywhere on this interface--not in the UAD Console app, not on the hardware, and not in the OS MIDI set up and other OS sound controls. The only way to get an input signal, seemingly, is to boost the input signal by boosting gain on the input channel, or to boost output by running output through the monitor outs, and increasing the monitor volume. Both of these methods produce unusable results due to what I assume is a feedback loop.

I have been able to produce intelligible graphs by running input through the interface, and output through the headphone jack on my Mac, and then using a headphone amp for extra gain (see attached). However, when using this work around, I am unsure if I am still getting a picture of the interface's frequency response, or the onboard sound card in my Mac, or neither.

Can I trust these results? Can anyone recommend another work around? Thanks.

 

[John Mulcahy]

Seems odd to not have gain controls somewhere, though you mention boosting gain on the input channel which is the control that would normally be used. There was a recent post on the UAD Apollo, but doesn't sound like the same thing. The measurement you posted looks fine, though something in the chain is inverting. You could use the monitor output but you would have to disable the inputs on the monitor path to prevent the feedback problem you saw.

 

[larrykohling]

Looks like using the monitor path worked this time. I cut the channel volume all the way, but kept it running to the monitor, and was able to get an input signal using channel preamp gain (not pictured) and monitor gain (pictured).

It looks like this new result doesn't have the same phase issue as the previous? Or at least not as extreme.

Thanks for the help.

 

[John Mulcahy]

Looks good. The phase on the previous measurement was +/-180 degrees due to the polarity change, no such issue with the new measurement.

 

[larrykohling]

Right on, thanks.