Crossing stereo and mono cables between multiple instruments

Question

My audio mixer comes with only one pair of mono phone jacks, which internally in the audio mixer are wired to come out as a stereo signal that goes to the computer on a USB cable.

The piano also has a stereo output that come out on two mono phone jacks, which appropriately go into the audio mixer's two mono phone jacks and all this works fine, stereo recording is achieved by the computer.

However every time I need to add another intrument to the mixer, such as a guitar, bass or micorophone that have mono phone jacks, I have to disconnect the piano (at least one side of stereo), which is annoying.

I would like to have all the instruments connected at the same time.

What would happen if I added two mono y-connectors to each of the audio mixer's jacks, then connected two mono instruments to these two available mono jacks?

In this situation, the left piano jack would share the left audio mixer's jack with a mono instrument and the right piano jack would share the right audio mixer's jack. For a total of three concurrent instruments, i.e. one stereo piano and two mono instruments.

Would these mono instruments interfere with the piano's stereo sound? Would all the instruments lose sound level or quality or damage each other?

Indeed the mixer has two mono inputs. But it also has midi jacks, so for now I will change my configuration and have the stereo piano go through midi cables and use the two input jacks for the bass and the guitar. Not my favorite selection of piano sounds, but still good enough for now.

This way each instrument gets its own track and gets recorded concurrently.

My concern is not only about distortion or loss of sound, but I need to know if the y-connector configuration would actually damage the mixer, or even worse, the instruments sharing the same jacks.

Answer 1

This is a bad idea, not least of all because you won't be able to balance the instruments and piano properly.

What kind of stereo mixer has only two inputs all in all? That's not a mixer, it's a volume control. Unless there is some kind of input you are not utilizing yet. If that's the case, you'll likely be better off trying to connect your piano to that and getting the required connectors/adapters there instead of trying to multifeed your mono inputs.

Answer 2

Actually, it does not sound at all like you are talking about an "audio mixer" here rather than an "audio interface" or "soundcard".

Assuming that this is the case and that you have a soundcard with Midi input and two mono inputs, the proper way to do your recording is to first record the two instrument signals and the Midi track from the piano into your DAW: that's using all the inputs you have.

Now you complain that the piano sounds of the DAW are not sounds you prefer over that of your piano, but you don't need to use them!

Just plug the piano into your sound inputs for a second take of two tracks while you play back the Midi track you already recorded into your piano: the second take does not involve any human playing. You'll probably need to nudge the new tracks forward a bit until their timing matches with the old tracks (to compensate for record/playback latency of both Midi and audio).

So now you have four audio tracks which you can mix at leisure. It's "almost" like a multitrack recording except that you actually have been playing together in the first take already. You just needed an extra pass for converting the Midi recording to another audio signal with the help of your piano (or whatever sounds the DAW or some external Midi device can provide if you like that better).

This will likely work slightly better if your piano comes with USB Midi as a primary interface: in that case you don't have the latency of the standard 31250bps Midi current loop interface.

An illustration of that kind of technique (unfortunately with the sound track being German) can be found in this video about multitracking with Ardour.

Answer 3

I have to agree with user21054, this is a bad idea.

If you want to connect two instruments into a mixer that only has two mono inputs and you're OK with the instruments being mono, a better way to go about it is only use one of your piano's outputs to connect to only one of your mixer's inputs, and use only one output from another instrument into the other remaining mixer input.

Using nothing but a Y connector to sum a stereo signal to mono is a recipe for creating unwanted distortion and phase cancellation on each of your mixer's mono inputs.

As far as separating the stereo channels, you should be able to achieve this in your DAW by routing each mixer input to its own mono track, or by splitting the stereo track into two mono tracks.

I recommend saving up enough money for a mixer that has more channel inputs as that is the most efficient way of solving your problem so you don't have to worry about summing any channels before the signal hits your DAW.