Motu 624 as home dac for crossover of subs

[ehabheikal]

I want to know the experience of people using motu or even other multichannel studio dacs as a home dac

Is there a convenient way to change sources between usb and optical? Has anyone tried it with purifi or ncore amps which do not have dc protection and i think these interfaces go down to 0hz or DC coupling or something like this and can cause problems.

Does motu do crossovers, i am interested in it doing crossover for subs.

 

[andreasmaaan]

I used a MOTU soundcard to implement a crossover on one occasion as part of a live sound install (don't ask why...).

Anyway, it is possible, but not easy.

MOTU's software mixer offers all the standard filters (LP, HP, PEQ, shelf etc.) but with limited configurability and some strange, irritating limitations (for instance, the PEQ filters use "bandwidth" rather than Q and are modelled on some kind of weird analogue EQ, which MOTU advertises as a feature but which makes it hard to work with IMO).

The main difficulty, however, is that the LP and HP filters have fixed slopes which can't be changed by the user (BW12 IIRC, but I'm no longer 100% sure). This would be rather limiting if you were trying to use the system to integrate a subwoofer. (You could probably use third-party software that would do a better job, however, e.g. EQ APO.)

An overview of their mixer is available here. I'm sure there's also more detail in the manual.

As to your questions about input switching, IIUC you also need to do this through the software mixer. Not very complicated, but a bit more work than flipping a hardware switch.

I don't know about the DC coupling question. Would seem very strange if that were the case though.

 

[somebodyelse]

They do publish the API the software mixer uses to change things though, so if you can face a little scripting you can make a much easier interface for input switching and master volume. It might be easier to set up the filters that way too. I'm assuming the documentation is accurate - I've not tried it!
https://cdn-data.motu.com/downloads/audio/AVB/docs/MOTU AVB Web API.pdf
If you've got more skill you could make a remote control with something like an ESP32, buttons, maybe a shaft encoder for master volume.

 

[HighImpactAV]

I have the MOTU 624. You can't use it for crossovers because there is no way to delay the mains relative to the subwoofer.

You don't need to change sources between usb and optical. You can route both through the mixer and then out the same output. That way whichever source is active will automatically be playing.

I use mine exclusively with amps that are DC coupled and go to 0 Hz. I've never had an issue.

 

[ehabheikal]

They do publish the API the software mixer uses to change things though, so if you can face a little scripting you can make a much easier interface for input switching and master volume. It might be easier to set up the filters that way too. I'm assuming the documentation is accurate - I've not tried it!
https://cdn-data.motu.com/downloads/audio/AVB/docs/MOTU AVB Web API.pdf
If you've got more skill you could make a remote control with something like an ESP32, buttons, maybe a shaft encoder for master volume.

I actually chose motu or rather want it because of the web based interface and i have web dev skills, so yes api and direct http calls

 

[ehabheikal]

I have the MOTU 624. You can't use it for crossovers because there is no way to delay the mains relative to the subwoofer.

You don't need to change sources between usb and optical. You can route both through the mixer and then out the same output. That way whichever source is active will automatically be playing.

I use mine exclusively with amps that are DC coupled and go to 0 Hz. I've never had an issue.

I am out of my depth here, is it possible to add DC coupling to an amp? I have purifi and was planning on adding a hypex too but this is scaring me on audiophonics they specifically say dc coupling is not a part of hypex

 

[ehabheikal]

I have the MOTU 624. You can't use it for crossovers because there is no way to delay the mains relative to the subwoofer.

You don't need to change sources between usb and optical. You can route both through the mixer and then out the same output. That way whichever source is active will automatically be playing.

I use mine exclusively with amps that are DC coupled and go to 0 Hz. I've never had an issue.

https://www.audiosciencereview.com/forum/index.php?threads/motu-8a-measurements.2342/

here is the motu 8a model and being used for crossover, i think they are the same engine but different in/out to the 624

 

[somebodyelse]

https://www.audiosciencereview.com/forum/index.php?threads/motu-8a-measurements.2342/

here is the motu 8a model and being used for crossover, i think they are the same engine but different in/out to the 624

In that case it's being used as the crossover for a 3-way, so doesn't need a delay like you will with subs. You could always loop the optical back into the PC and do the crossover there before sending the 4 channels back for output - that would give you more options on the filters as well as letting you do the delay.

 

[ehabheikal]

?

In that case it's being used as the crossover for a 3-way, so doesn't need a delay like you will with subs. You could always loop the optical back into the PC and do the crossover there before sending the 4 channels back for output - that would give you more options on the filters as well as letting you do the delay.

Why does a sub need delay?

 

[andreasmaaan]

In that case it's being used as the crossover for a 3-way, so doesn't need a delay like you will with subs. You could always loop the optical back into the PC and do the crossover there before sending the 4 channels back for output - that would give you more options on the filters as well as letting you do the delay.

I would certainly trust your knowledge as to the 624 specifically. Not sure about other models. I seem to recall having delays on whatever MOTU it was that I did this on, although it is possible that I didn’t (which would further explain why it was such a painful process).

 

[andreasmaaan]

?

Why does a sub need delay?

It doesn’t in all cases necessarily, but if it doesn’t, that will be a lucky coincidence.

Delay allows you to control the relative arrival times of the outputs from the speakers vs the sub so that they integrate optimally.

 

[somebodyelse]

I would certainly trust your knowledge as to the 624 specifically. Not sure about other models. I seem to recall having delays on whatever MOTU it was that I did this on, although it is possible that I didn’t (which would further explain why it was such a painful process).

Don't take my word for it - I don't have one so I'm just going by @HighImpactAV's comment as an owner. The 8A was looking very tempting (the API especially) until I found reports of flaky UAC2 operation of the whole AVB family with linux.

 

[ehabheikal]

Don't take my word for it - I don't have one so I'm just going by @HighImpactAV's comment as an owner. The 8A was looking very tempting (the API especially) until I found reports of flaky UAC2 operation of the whole AVB family with linux.

Damn, actually linux is important for me 2. use it a lot.

 

[somebodyelse]

See this post from the 8A thread for the linux issues - it was a while back now so things may have changed.

 

[HighImpactAV]

https://www.audiosciencereview.com/forum/index.php?threads/motu-8a-measurements.2342/

here is the motu 8a model and being used for crossover, i think they are the same engine but different in/out to the 624

There is more info in the thread. He is using the MOTU as a DAC, but the crossover is being done by Audiolense and it's convolution filter in software. The MOTO DSP isn't being used for the crossover.

 

[HighImpactAV]

?

Why does a sub need delay?

Even if on the same plane, the mains will typically need a delay. Both passive and analog filters add delay to the signal. This article on time and phase alignment might help.