Question regarding ADAT lightpipe - Focusrite Clarett 8pre

[Stig Ø]

I've ordered a new interface - Focusrite Clarett+ 8pre - and I'm thinking about connecting my UA 4-710D preamp via ADAT optical. If I understand it correctly, the usual solution for latency-free monitoring is to have the montor signal pass through the interface directly without AD/DA conversion. Will latency and monitoring be a problem with the ADAT connection? The alternative is to just go line out from the 4-710 into the analogue inputs of the Clarett.

On the subject of Focusrite, is it possible to reverse polarity on that unit? I've been over the manual for both the interface and the Control software, but I haven't seen any switch (hardware or software) which enables this. I have a mic that needs polarity reversal, so I have to figure out a way to do this.

As always, any tips greatly appreciated

Stig

[Hugh Robjohns]

I'm thinking about connecting my UA 4-710D preamp via ADAT optical. If I understand it correctly, the usual solution for latency-free monitoring is to have the montor signal pass through the interface directly without AD/DA conversion. Will latency and monitoring be a problem with the ADAT connection? The alternative is to just go line out from the 4-710 into the analogue inputs of the Clarett.

Latency free monitoring normally only involves the analogue inputs. So your latter suggestion would be fine.

I can't see in the manual whether the ADAT inputs are included, but I strongly suspect not as it would require a set of 8 D-As...

On the subject of Focusrite, is it possible to reverse polarity on that unit?

Not that I can see. I imagine they expect that to be done in the DAW.

I have a mic that needs polarity reversal, so I have to figure out a way to do this.

Invest in an XLR barrel (inline) polarity (phase) reverser! I think Shure, whirlwind and others make them (Make sure pin1 is connected st both ends — some 'line level' ones don't!)

Best value is probably the Hosa GXX-195. Costs around £10. The blurb says its for line level signals, but it's fine for mic signals too, and pin-1 is connected.
Amazon UK here

Or if you can solder, make up your own dedicated polarity reverse cable. You just need to swap the signal wires on pins 2/3 at one end! ... and label it clearly so it doesn't get used where it's not needed!

[Stig Ø]

Thanks for that quick and thorough reply. Seems I'll be going analogue then. Didn't quite understand what you meant with the ADAT in - there is an optical out from the UA preamp, and an optical in on the Clarett, but seems like latency-free monitoring is out anyway when using that, so I'll just go with the analogue inputs. Great tip about the inline thingie - didn't know they existed! Thanks again.

Stig

[James Perrett]

You would probably add less than 2mS of latency by monitoring via the optical connection which most people would find inaudible. However, I don't know what monitoring facilities are offered by the Focusrite interface and whether it can monitor directly from the ADAT inputs.

[Stig Ø]

Thanks, James. 2ms sounds quite tolerable. I'm not sure about the monitoring either, but it seems to be the recommended way to expand inputs by, e.g., using the Octopre in Focusrite's literature, so I would kind of expect it to be possible. As I understand the documentation, the ADAT channels from an external source pops up in the output routing/mixing software just as any hardware input channel would. I'll know as soon as I get my hands on it - it's being sent today. Will post back here and in the "can't believe it's another interface question"-thread which is where this whole thing started.

[Kwackman]

Thanks, James. 2ms sounds quite tolerable.

2ms is the equivalent of moving your speakers back 2 1/2 feet (I think!)

[Stig Ø]

Yes, 2ms is not much and probably wouldn’t bother me. I think rule of thumb is a foot/ms or thereabouts.

[Hugh Robjohns]

Using the ADAT optical ports for additional inputs is a great way to expand an interface. No problem with that.

The question is whether the latency-free mixer (which normally routes analogue inputs directly to the headphone output bypassing the computer and thus its associated latency) can access the ADAT inputs directly.

I fear not... mostly because to do that it would need a set of D-A converters to directly convert the ADAT signals to analogue to then blend in with the local analogue sources. That's a lot of effort and expense to introduce on a feature that few would normally require.

...but if it did work that way, you would have around 1-2ms of latency (depending on sample rate and converter types) as James says due to the A-D converter in the external preamp and the D-A converter in the interface. And up to 2ms is generally unnoticeable to guitarists, keyboard players, and drummers, and tolerable to most singers.

More likely, though, the ADAT signals will be routed straight into the computer, and then back out again along with any other computer DAW sources... adding considerably to the roundtrip latency!

[Stig Ø]

Using the ADAT optical ports for additional inputs is a great way to expand an interface. No problem with that.

The question is whether the latency-free mixer (which normally routes analogue inputs directly to the headphone output bypassing the computer and thus its associated latency) can access the ADAT inputs directly.

I fear not... mostly because to do that it would need a set of D-A converters to directly convert the ADAT signals to analogue to then blend in with the local analogue sources. That's a lot of effort and expense to introduce on a feature that few would normally require.

...but if it did work that way, you would have around 1-2ms of latency (depending on sample rate and converter types) as James says due to the A-D converter in the external preamp and the D-A converter in the interface. And up to 2ms is generally unnoticeable to guitarists, keyboard players, and drummers, and tolerable to most singers.

More likely, though, the ADAT signals will be routed straight into the computer, and then back out again along with any other computer DAW sources... adding considerably to the roundtrip latency!

I see there is more to this digital recording malarkey than I realised. Thanks for explaining that so that I understood it. Just curious, how do people fix the monitoring with input expansion? Monitor through a mixer?

[James Perrett]

More likely, though, the ADAT signals will be routed straight into the computer, and then back out again along with any other computer DAW sources... adding considerably to the roundtrip latency!

I've not actually tried it with my Focusrite interface, but I would have assumed that the interface would handle the monitoring digitally so that all the signals would be digitised, then attenuated and routed digitally to the headphone or monitor DACs. So the zero latency monitoring still includes the latency from A/D and DAC.

As I understand it, this is how RME's Totalmix works and I would have thought it made sense for other manufacturers to do this digitally rather than have a chip containing a large analogue routing matrix.