computer interface

Hello fair fellow members of the Recording Equipment forum!
I’m looking for a piece of hardware and I don’t know if such a device even exists, or if I should attempt to build it. I’m looking for some sort of computer interface. I’m working with an existing PA system at a local church, the amps are all in place, the mixer is already there, and I’m looking for a way to be able to record the channels each separately and remix/postprocess later. The recordings are presently dumped directly to audio-cassette and the results on the tape are somewhat unpredictable when more than one channel is at use at a time.

What I’m hoping for is basically a box with XLR inputs and outputs, that can pass through the signal and the phantom power for the mics. But inside the box I think I need an ADC (how many bits I don’t know) and a bus to get the data to my laptop. I have USB 2.0 and Firewire inputs on my laptop, and if I need to write some software I can do that. Simple pass-through for the existing house mixer is important, but not a feature I’ve seen on any existing mixer or interface. What I’d like to see when I’m recording is anywhere from 5 to 16 oscilloscopes and signal meters on my laptop screen (so I know what channels are in use). The device does not need to do the recordings itself if the USB/Firewire/other bus can handle the data being moved.

If such a solution exists I don’t even know where to look for it. It doesn’t necessarily need to real-time effects processing, I don’t know we’d ever use it. I just want to remix for audio recordings after the service instead of trying to badly mix the service and recording simultaneously.

Thanks for your help!

I’m surprised one of the requirements is not to hand out CDs as people are leaving. Believe it or not, that’s the normal request and some people get startlingly close with a high-speed duplicator.

I need to study this. Multi-track is a little rough because many “multiple channel” devices are really a bunch of stereo devices in a box – and Audacity only recognizes one stereo device.

The phantom thing is going to be interesting…


So I kinda am looking for a four-track recorder in a PC digital-audio interface, that takes a raw signal before the front-of-house mixer and samples it.

I figured getting around the phantom power would be easy, either a DC-block on a DI box or a diode to protect the ADC on a breadboard. Worst case optocoupler.

I figured Audacity was how I was going to re-mix later, even if I had to repeatedly add one channel at a time.

End-of-service recordings of just a sermon would be easy, a pastor sermonizing only uses a single mic. Normalizing helps with crappy lapel mics, but a headset mic is definitely preferable for voice recording. It keeps the levels consistent.

Start by telling us in more detail what you already have - specifically the mixer. Does it have direct-outs for each channel? Does it have inserts on each channel (these can be used a direct outs). How many channels are you using? Is it a 4-bus or 8-bus mixer, and if so can you do sub-mixes?

My thought is to avoid mic splitters and tap the line level signals coming out of the mixer. Then “all” you need is an 8-channel USB audio interface - one that Audacity will recognize. There’s the rub. As Koz points out, Audacity is kind of picky about the audio interfaces it will talk to.

You may already be beyond Audacity’s capabilities. What computer will you be using to record the services?

– Bill

The mixer is the part I know the best, as I do most everything on it. It is a Peavey Unity 2002 RQ-16. At the top of the board are XLR and TRS inputs (is that what you mean by inserts?) This is a pretty simple board, it does what they need and not a lot extra. They use 4 electret condenser mics plus two wireless mics, another mic on the piano and one on the lectern. That’s 8 channels. Plus two people play guitar, and there are a tape deck and CD player tied to the board too. We’re up to 12. There’s a couple channels that are wired up as just remote XLR ports – these just sit silently waiting for another mic to be plugged in at a different place on the stage (altar area.)

As mixers go, this isn’t overly complicated. Top to bottom we have per channel
High EQ
Mid EQ
Low EQ
Monitor A
Monitor B
Effects A
Effects B
Pan (must be centered)
and a fader slider.

Monitor A is actually used for a monitor for the singers.
Monitor B is wired to a transmitter for wireless headsets for the hearing impaired.
EFX A is connected to a tape deck.
EFX B is available.

The board does have (2) EFX return inputs off to the side, but we don’t use them.

EFX B is where I connect to my laptop’s mic jack, and then record that way using very low volume settings on the mixer and adjusting the sensitivity on the laptop.

It works, for the most part. But I’m recording the output after I’ve already mixed the channels using the row of knobs for EFX B. Problem is, I don’t have 3 independent sets of ears on my head to monitor the tape, the laptop, and the house output.

The collection of amps are all tied to the house ouput (Master Left Fader).
The mixer has a built-in preamp that drives the mics. There is a “Phantom Power” switch on the board that is taped down and labeled that it must remain on to supply +48V to the mics.

All but two channels (tape and CD) are connected using the XLR inputs.The manual says we can’t use both the XLR and the TRS connectors on a given channel simultaneously. TRS is high impedance, XLR is low-impedance. Did you suggest that I should be able to get a raw per-channel signal by connecting to the balanced TRS inputs (using the TRS input as an output)?
Would getting an external preamp allow me to tap the signal between mics and mixer?

Thanks again!

That’s a very old mixer (1998 according to the Peavy web site). It does not have channel inserts nor channel direct outs.

It seems from your description that you want to be able to record up to 16 separate channels (stereo tape/CD each count as 2 channels), then mix those down to a stereo show. I am not aware of any system short of Pro Tools HD that will do that.

The mic splitter that you are thinking of building has many pitfalls. Use of diodes or opto-couplers to isolate the phantom power will destroy the audio. Getting multi-channel audio into your computer over USB in a format that any other audio editing software will recognize is not a trivial problem.

You could upgrade your mixer to a 4-bus or 8-bus type then record the sub-group outputs. For this you could use any of a number of 8-channel USB or Firewire audio interfaces. That’s the way I’d go. You’re talking a couple of thousand dollars in upgrades here.

The problem remains of getting Audacity to recognize the 8-channel interface and record the 8 channels simultaneously. On the Mac side I’ve been told that Logic Express is pretty good at talking to just about any multi-channel interface as long as it uses Core Audio.

– Bill

Reading more closely, I think you are making this more complicated than it needs to be. Remixing every service will be very time consuming, plus expensive to implement.

EFX B is where I connect to my laptop’s mic jack, and then record that way using very low volume settings on the mixer and adjusting the sensitivity on the laptop.

This is problematic. First, you have a mono signal from EFX B. Second, you are introducing noise from the microphone input of the laptop. Third, you run a real risk of overloading the mic input on the laptop and getting distortion. Why not feed the laptop from the Tape Outs of the mixer through a Behringer UCA-202? Or at least feed the EFX B output to a UCA-202?

I understand the need to provide a separate recording mix. Not everything needs to run through the PA, or some sources need only “reinforcement” using the PA.

the results on the tape are somewhat unpredictable when more than one channel is at use at a time

Sounds like you’re having trouble controlling vocal levels. An option is to upgrade your mixer to one with channel inserts and buy 8 channels of hardware limiting to patch into the problematic channels. This will “tame” the problematic channels, resulting in a more consistent mix.

In short, IMHO you’re attacking the problem from the wrong end. Rather than make a multi-track recording that you need to remix, implement a setup that provides an adequate stereo mix to the recorder. This will save you oodles of time, and probably be cheaper. It might be worth talking to someone from a local pro audio shop and see what they recommend. Without actually seeing (and hearing!) your installation, I can’t really make any informed recommendations.

– Bill

Simultaneous recording of more than 8 channels is expensive. The Boss BR-1200CD is one of the cheapest devices that claims to manage 12 simultaneous channels (about $900 US). 8 channels or less can be a lot less money. Alternatively, improving your live mix so that you have a good enough mix to be recorded in 2 channel stereo may be a viable option.