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I am looking for an ideal setup given what I've got. I'd like to send my guitar through my Digitech RP500 multi-effects pedal, then through my M-Audio M-track device, which is connected to my PC via USB and also outputs to my two monitor speakers.

I've tried setting it up as follows: - 1/4" from guitar to RP500 input - 1/4" Y-cable from RP500 outputs (right and left) to M-Track guitar line input - M-Track device sends signal to PC via USB and back to device - 1/4" Y-cable from M-Track outputs (right and left) to monitors

Setting it up this way seems to result in little signal from the RP to the M-Track... but taking out one RP output (so that it's just either mono or stereo) seems to improve it. What's going on? The RP also has it's own USB, perhaps I could skip the M-Track altogether?

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Why would you think you need a Y-cable for this? Each of the M-Track's inputs is mono, so it's no use to feed them a stereo signal. If you tried this with an unbalanced input, like in a guitar amp, you'd get only the left channel from the Y cable, because only the tip of the 1/4" is considered: the ring is either left open, or even short to the grounded shaft.

However, as in any decent interface, the M-Track's line inputs are balanced. That means, it actually considers both the ring and tip signal – but it doesn't mix them as you seem to think, but subtracts them. (Read the Wikipedia article if you want to know why this is done.)
So if you're feeding it a headphone-style Tip/Ring=L/R signal, you end up with only the stereo difference. And for a normal dry-ish guitar signal, that's not a lot: normally, electric guitar is “almost mono”, any side components come mostly from reverb, delay or modulation effects. But the mono components are cancelled when you subtract the L and R channels, and the result is “silence with reverb”.

What you should do instead is, use two lines, one for each channel. Ideally make them both TRS cables, so you actually get the benefits of the balanced ports (but ordinary guitar cables should also be fine). Alternatively – it seems the RP500 has indeed an audio interfact built in, you can try connecting that directly via USB.

That's not what I'd do though: if the “amp” is digital anyway, you might as well calculate it later on, i.e. in a software plugin loaded in the DAW. That gives you much better flexibility, and allows tweaking the sound later on without re-recording, if you find it doesn't fit as good in the mix as you though. So I'd only record the unprocessed guitar signal, right into the M-Track's guitar input. Then either record completely clean, or, if you prefer use the RP500 as a mere monitoring-rough-processor that's not actually recorded.

  • Thank you for your detailed response! If I record straight through the M-Track as unprocessed guitar signal, how do I go about using the RP500 solely for digital effects post-recording (i.e. "as a mere monitoring-rough-processor that's not actually recorded"). – Liam A Mar 2 '15 at 22:29
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    You can do that either by connecting the RP500 via USB and somehow soft-routing it as an FX plugin (not sure if/how it works with that model), or you can plug one of the M-Track's outputs back into the RP500's guitar in and record from its stereo out. The technique is called re-amping, you can look it up for further advice. — However, the main idea behind my suggestion to record the clean guitar signal was to not use the RP500 at all in a way that's audible in the final result. I would instead do all FX, amp-simulation etc. with software plugins in the computer. – leftaroundabout Mar 2 '15 at 22:44
  • Any suggestions for user-friendly post-FX software? – Liam A Mar 2 '15 at 22:57
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    My favourite for distortion/amp stuff in particular is iZotope Trash. In general for virtual effects, the plugins included in Reaper are a great starting point, and they're actually gratis! – leftaroundabout Mar 2 '15 at 23:04
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The M-Audio M-Track is a computer interface to allow you to input audio and instrument signals into your computer.

The Digitech RP500 is a multi-effects processor for guitar - which also provides for input of the processed signal into your computer.

The Digitech RP500 provides for the output to be summed as a mono signal and sent to a guitar amplifier, or the stereo signal can be sent to a full spectrum PA or monitoring system (ideally through a mixer) or the signal can be sent to your computer via the USB output and recorded into any number of DAW software programs.

You don't need to use the M-Audio interface with the Digitech RP-500 because it can input the processed signal into your computer directly. Running the signal through the M-Audio first could potentially introduce extra latency since the M-Audio must process the already processed signal before sending it on to the computer.

For the application you described - connect everything as follows:

  1. Plug guitar cable from guitar - into the instrument input jack on rear of RP-500.

  2. Using an XLR cable - plug your left monitor into the left output and your right monitor into the right output. If using a mixer you will plug into either the left and right input of a stereo channel or pan one channel hard right and the other hard left. If your monitor speakers only have 1/4" inputs, use the 1/4" outputs.

  3. Connect the RP-500 to your computer using the USB jack.

  4. Before turning on any power - set the volume controls on your speakers and on the RP-500 to zero. Then gradually increase the volume.

You can also monitor the output of the RP-500 through headphones (jack on rear of unit).

If you were going to run the signal from the RP-500 through the M-Audio on the way to the computer, (not necessary) I would suggest using a TRS cable to make the connection. If you only use the left output on the RP-500 - it will sum the signal into mono. If you use both outputs (two cables) it will send a stereo signal. If you are connecting to a single source input such as a single guitar amp or single monitor speaker, you will need to use just one cable plugged into the left output jack.

If you have the M-Audio M-track device that has a stereo/mono switch, you can feed the left output from the RP-500 into the left channel of the M-Audio and the right output into the right channel. If your M-track does not have a stereo feature (some models) you will be sending a mono signal only so use only one cable from the left output of the M-Audio. When using the 1/4" outputs from the RP-500 you must select either the amp mode or the mixer mode using the switch beside those output jacks. The amp/mixer switch will affect the gain of the signal being output.

Using a Y cable will not give you good results because the circuitry inside the RP-500 is set up to recognize which output jacks are active and if only one cable is plugged into the left output only - it automatically switches the output to summed mono.

In summary, the M-Audio interface is not required for the application you described nor is it recommended. To use a non electronic analogy, if you want to pour salt out of a 5 pound bag into a salt shaker, you could use a funnel to direct the salt into the salt shaker. But one funnel is all you need. If you poured the salt into one funnel to pour salt into a second funnel - you still get the salt into the salt shaker - but you don't gain anything by using two funnels. If anything it slows the process.

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