Author Topic: Unwanted noises  (Read 84 times)

Angus Byrne

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Unwanted noises
« on: December 02, 2019, 05:49:44 PM »
Hi

Iím getting occasional and, seemingly random, high-pitched squealing during use. I have the Gecho audio running into a track on Ableton live and, occasionally, this sound simply changes into a high-pitched electronic squeal. Although this is random generally it is guaranteed to happen fairly quickly once I plug a USB lead into the unit for power. Switching off and on gets rid of the noise but, eventually, it comes back.

Any thoughts?

mario

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Re: Unwanted noises
« Reply #1 on: December 02, 2019, 08:19:52 PM »
Hi Angus,

Hard to tell without hearing it (maybe you can post an audio file?)

What is it powered from? Maybe it is a ground loop / bad voltage spikes / interference throwing the internal circuitry off?

What is playing - is MIDI involved? Some channels go haywire with high enough MIDI notes. There are no checks in place to tell if values calculated after the chord expansion (as explained here in the "MIDI Polyphony" paragraph) still make sense for the particular engine, but that would not be connected to USB powering in any way.

If it is indeed MIDI related and you could isolate the issue to the simplest possible scenario (e.g. note x in channel y always does this) then it would help a lot to replicate and fix.

Cheers,
Mario

Angus Byrne

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Re: Unwanted noises
« Reply #2 on: December 04, 2019, 03:47:25 PM »
Hi Mario

Iíve attached a video clip showing the problem. The Gecho audio is going into Ableton and the Midi is coming into it from a Push 2 via the studio MOTU USB MIDI interface. The squealing continues even when Reset is pressed and the channel (31 in this case) is closed.

I donít have any similar issues with any other kit in the studio.

Cheers

mario

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Re: Unwanted noises
« Reply #3 on: December 05, 2019, 08:00:36 AM »
Hi Angus,

The attachment did not upload, maybe it was the file size limits which I've just increased.
You can also send it to me via email if this still does not work.

Does the noise only occur when powered from USB?

When nothing plays, codec is muted and Gecho does not emit any sound, obviously the noise does not originate there but is caused by a ground loop or such. Maybe your other devices are powered via transformers so they are galvanically isolated. MIDI is also isolated (optically) but in Gecho the same connector is used for other things, hence it has a ground potential at the "sleeve" and this may be one of the paths via which the ground loop is created.

You may need to use a ground loop isolator or for the USB power, one of these.

But this is all just my speculation, seeing / hearing it would help a lot.

Cheers,
Mario
« Last Edit: December 05, 2019, 08:34:11 AM by mario »

Angus Byrne

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Re: Unwanted noises
« Reply #4 on: December 05, 2019, 11:37:07 AM »
Thanks for your reply Mario

Iíve sent a video clip to [email redacted by admin to not attract spam]

The noise happens when USB isnít connected.

Cheers
« Last Edit: December 06, 2019, 05:11:19 PM by mario »

Angus Byrne

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Re: Unwanted noises
« Reply #5 on: December 05, 2019, 03:12:01 PM »
Well, itís not a very nice day outside here in the north-east of England so Iíve had another run with MIDI into the Gecho.

I first tried running MIDI directly in, bypassing the computer, Ableton and the Motu MIDI interface - and it worked! (On channels 31 and 34.) This was with USB power plugged in. So, I tried it with MIDI coming from the MIDI interface via Ableton - and that worked as well. In fact itís running and making some very interesting noises as I write this. Iíve made another video clip demonstrating this and will send it by emai since itís too big for this forum.

A second test, sadly, threw up the same issues as previously 😟

I wonder if itís just a slightly insecure connection on the MIDI in socket? Or am I not using the right routine for connecting USB power? BTW, is it to be expected that plugging in USB power while using a channel should make the Gecho stop?


Cheers

mario

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Re: Unwanted noises
« Reply #6 on: December 05, 2019, 04:06:10 PM »
Hi Angus,

Thanks for the videos. It is really a horrible high pitch sound.

Quote
I wonder if itís just a slightly insecure connection on the MIDI in socket? Or am I not using the right routine for connecting USB power?

-- I don't think it's either, MIDI over this kind of cable is very reliable, and USB should not have any influence at all. Apart from ground loops which can be introduced by plugging in any of the cables. For example, if you power two devices from USB ports of the same laptop, it is very common to lead to such problems (but not what I hear on the videos, that sounds completely different).

Quote
BTW, is it to be expected that plugging in USB power while using a channel should make the Gecho stop?

-- not at all, unless it is a PC, which will try to reset it as the driver assumes it is a serial modem which needs to have "request to send" handshake signal triggered (it may depend on the OS but Windows does that for sure).

I had impression that you are playing it on monitor speakers, is that correct?

Cheers,
Mario

Angus Byrne

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Re: Unwanted noises
« Reply #7 on: December 05, 2019, 05:49:23 PM »
Yes. Iím using KRK VX8 monitors. Iím aware of the potential for feedback so have made sure thatís not an issue.

Thanks

mario

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Re: Unwanted noises
« Reply #8 on: December 05, 2019, 06:27:21 PM »
It sounds like audio feedback to me.
Are mics off / does it do the same thing then?

mario

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Re: Unwanted noises
« Reply #9 on: December 06, 2019, 05:08:39 PM »
Upload test...

mario

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Re: Unwanted noises
« Reply #10 on: December 06, 2019, 07:28:52 PM »
Hi Angus,

I've analysed the video you sent, for example at 1:13 where you just started channel #31, there is immediate high pitch sound, with peak at 8471Hz. If compared to sampling rate that channel runs at, this gives 50780Hz / 8471Hz = ~5.9946 which is suspiciously close to 6. That means, there is signal that resonates at every 6 samples. It even increases between 1:12 and 1:13, following a standard ramp-up that every channel begins with:



Or here at ~0:10, there is peak at 6359Hz, which again, when dividing 58780Hz, gives ~7.9855, close to resonating at every 8th sample:



So, what we can conclude is that this originates from codec or before (at input) and it isn't something that happens between the device and the rest of your audio chain.

A device with close to zero latency will inevitably fall into this kind of feedback when played loud. You mentioned that the unwanted noise does not happen immediately, only after you play some of the higher notes - and indeed after you do that, it changes - which is only logical (while in #31 granular or #34 Clouds) as that means there is some pitch shifting of the input signal going on.

Sometimes the buzzing is there from the very beginning. It may depend whether a certain channel clears delay buffer or not (this was intentionally left as is, as it often creates interesting results when you run one channel after another).

What you can do to confirm or rule out the possibility that this is simply an audio feedback / Larsen effect, is to press RST+B4, then the buzzing should decay in a few seconds (or not).

Also, is there any difference when you switch the output between Line level and HP level?

Cheers,
Mario
« Last Edit: December 07, 2019, 06:42:41 PM by mario »