Topic: Solved thankyou - Firewire interface with SD702

[JackHenry]

My normal recording is a stereo pair direct into a Sound Devices 702.

I'm thinking about getting an 8 channel firewire pre-amp mixer for my laptop for some different recording I want to do.

I also may use it with the 702. I've looked everywhere online to find the use of the AES/SPDIF input on the 702 without success. If the firewire pre-amp/mixer that I choose has AES/SPDIF out, is this the best way to
connect it to a 702? If so, is there any benefit or disadvantage of doing it this way?

Regards
John

[notlance]

Your situation sounds very familiar to me; I also have a SD 702 and I wanted to record more channels.  So I bought a PreSonus FireStudio Project (8 mic inputs, SPDIF in and out, bunch of other stuff) to connect to my laptop.  I’ve used the PreSonus for some location recording with mixed results.  I record 90% acoustic/classical and although the mic preamps aren’t bad, I did not think they were quite good enough.  They also will not supply 48V phantom to more than two mics at a time; once you connect more than two condenser mics, the voltage drops to about 35V.  For many mics that is not a problem, but for my primary mics, it is.

My main concern, though, is the delicacy of laptop location recording.  Laptop recording has too many Single Points of Failure (SPOF).  You are just one glitch from disaster, and I was never comfortable with that.  This is not a problem with the PreSonus in particular, but with laptop location taping in general.  Now if you are not taping live on location it is much less of a problem.  For a home studio the PreSonus and gear like it are just fine.

I guess I have been spoiled by my 702.  The bottom line is I bought a 788T to do multiple mic location recording.  Not an inexpensive solution, but it works for me.

Anyway, getting back to your questions, I have never connected my PreSonus to my 702.  In fact, I’ve never thought of connecting them until you brought it up.  When I connect the FireStudio to my laptop, it is controlled by a PreSonus app and Cubase (DAW software) running on the laptop.  Of course the 702 is not running any apps or DAW software so I doubt you could connect the PreSonus to a 702 via FireWire.

The only information I have on the 702s AES/SPDIF input comes from Page 15 of the 702 manual.  It appears you could connect the FireWire pre-amp to the laptop and run the app to control it, and connect the FireWire pre-amp’s AES/SPDIF output to the 702.  However, why would you do that?  To use the 702 as a bit bucket?  Why not just record to the laptop since you already have to use it to control the FireWire pre-amp?  Maybe I do not understand your application.

Even though I have not given it a very good sales pitch, I’d be happy to sell you my PreSonus if you want to play around with something like that.  It is an inexpensive way to record lots of tracks.  PM me if you are interested.

[JackHenry]

Thanx for that information.

I'm kind of surprised that you have difficulty powering more mics with phantom power. I don't know that unit so forgive this question. Is this problem a result of powering it via the firewire bus? Or are you connected to mains power?

I understand that the 702 firewire will only be used for file transfer and I
can't imagine that would be an easy change. But as I said, information is thin
on the use of input via the AES/SPDIF connection.

The vast majority of my recording is two microphone direct to stereo via the two xlr inputs on the 702. Recently, I've been asked to record something that may need more microphones (string quartet, choir etc) So I'm looking for a way to use the 702.

I could use a firewire interface into my laptop, but as you mention the SPOF's increase considerably (I know many will argue that's not the case, but that's not my question here). I'm aware of how to do it via the laptop. My question relates specifically to using the SD702 with an external device.

I'm also aware that the firewire connection on the SD is only fo file transfer to a computer or external FW Drive. So, with those parameters in mind, can a device that I purchase for firewire connection to my laptop (a seperate issue) also be used for connecting more that two microphones into my SD702.

Specific information about use of the SD702 AES/SPDIF input is a bit rare.

The way I understand it (and I'm possibly wrong) is that if I have something
that will output via AES/SPDIF, I can input it direct to the 702 via the same.
So I could use more that two microphones into an external mixer/amp (such as the
motu traveler) and then via it's stereo AES/SPDIF into the SD702 AES/SPDIF
input. OR do I need to use the SD702 XLR inputs (at line level) to achieve the result I'm after?

The nice thing about the traveler is that it can be bus powered from the laptop (if I'm using that method)
or battery powered for use with the SD702. This frees up my reliance on mains power allowing me to record in the middle of a forest if needed.

Can anyone correct me if I'm wrong please.

Just a note on the 788, I see that it can now do 12 tracks via the firmware upgrade.

[notlance]

OK, now I think I know what you are trying to do.  It appears the MOTU Traveler can work as a stereo mixer for your 702 or a many track FireWire interface to a laptop.

If you are using the Traveler as a mixer feeding your 702, the question is which has the better A/D?  If you think the Traveler’s A/D is better, use its AES/SPDIF output, otherwise, use the line out.  Try them both out and use the I/O that sounds the best.

I bet you can connect the Traveler’s AES/SPDIF output to the 702’s input and it will work fine.  However, I’ve never used the Traveler so I’M JUST GUESSING.  If all else fails you can just go line out/line in; that’s gotta work, right?


To answer your question about my 48V phantom problem, my FireWire interface in mains power only, so it’s not a problem of not enough juice through the FireWire interface.

And yes, the 788T can record 12 tracks, but it has “only” 8 inputs so those extra tracks can only be mixes of those 8 inputs.  For the type of recording I do, 8 inputs are plenty.

[ghellquist]

Some notes. I run a RME Fireface 800 but the most things should apply to other boxes like the Motu-s.

The 702 allows you to record what comes in to the AES input. This can be an external mixer with AES output or for that matter one of the Firewire interface (like the FF800).

My FF800 works like this, and I believe the MOTU works the same.
   1 - the inputs are converted into digital (AD-conversion)
   2 - the digital signal is handled internally by the built-in processor.
   3 - the signals can be mixed together
   4 - the result can be sent out to the AES output.
It is possible, at least with the FF800, to "burn" a mix setting that will come into effect on power up.

You will face two problems when using an external box without a computer like this as external inteface.
a) how do you set levels and panning
b) how to you listen to separate channels in order to track down problems

With the FF800 there is no front panel control of levels and panning. But it is possible to use an external midi controller, one example might be a Behringer BCF2000. Not sure if this applies to the Motu.

I believe using a laptop is a good solution. The laptop then has two purposes.
 1) primary recording device, recording all channels.
 2) controlling the mix going out to AES.

I know the FF800 rather well. If the computer stops it sometimes stops passing sound through the internal mixer, but most often it simply goes on passing signal. In this case the 702 would be the backup recorder while. Not sure what the Motu would do.

Gunnar

[JackHenry]

Excellent answers.

Thank you both, that has answered most of my 'issues'

I had assumed I'd use the line out/in scenario, but then I started wondering about the AES/SPDIF. Having not used it, I thought I'd ask in an area where someone must have already invented the wheel before me.

From reading the information about the traveler, it seems that I can probably mix 'in the box' without a laptop, but I'll download a manual for it. I only mention the traveler as that's what brought my attention to this method. I still need to research the actual product to buy some more.

Thanks again
John