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Reducing noise from keyboard output?

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Reducing noise from keyboard output?

Postby ultraGentle » Thu Feb 25, 2021 4:43 pm

I have a Casio CDP S350, which, unfortunately, has only a headphone out (3.5mm).

More unfortunately, the headphone out is quite noisy -- and not analog noise hiss, but a horrible digital (?) static plus a constant F4 tone.

I'm wondering if anyone has ideas on how to capture cleaner output, short of selling the keyboard!

Recording of said noise, with keyboard plugged into audio interface via 3.5mm TRS --> 1/4" TR, TS: https://filebin.net/o37el81q514qhd1j/ca ... t=mqvmpzte (link expires March 2nd, in case this is viewed in the future).

The signal from headphone out is extremely hot when plugged into an audio interface, so one thought I had was to simply gate the keyboard so that when playing, the signal overwhelms the noise -- but then the noise creeps back in on note decays.

Confounding factors, if I plug the headphone out directly into my monitors 3.5mm analog input, the noise is much quieter compared to monitoring through my AI. Similarly odd, I once plugged the keyboard into a Zoom Livetrak L8, which also has a dedicated 3.5mm input for phones, and then the noise was again largely absent, and instead, there was a kind of old-film-reel ticking in the background, which was less offensive.

I'm wondering if the comparative lack of noise via 3.5mm cable has something to do with the stereo-ness of the signal, but honestly, I'm drawing a blank. I could record my monitor output, but that's quite cumbersome and convoluted.

Has anyone encountered this? Suggestions?
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Re: Reducing noise from keyboard output?

Postby Sam Spoons » Thu Feb 25, 2021 4:52 pm

Small keyboards often have double insulated power supplies so it may be that adding a decent earth connection somewhere in the system might solve the digital noise problem (obviously if you are using a desktop computer or any other piece of kit with a good earth the disregard that suggestion)?

Remember too that a headphone output is stereo/unbalanced the inputs to most interfaces are balanced though if the headphone signal is strong that is unlikely to be the issue. Your explanation of the cable you use is unclear but if it is 3.5mm TRS to 2 x ¼" TS you are fine.
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Re: Reducing noise from keyboard output?

Postby ultraGentle » Thu Feb 25, 2021 6:58 pm

@Sam, forgive the naive followups, here, but:

> adding a good earth connection...
The keyboard has a two-prong plug and is connected to a power strip/surge protector that does have a ground. Have I thus implemented your suggestion already, or is there another point in the keyboard/recorder/power system that might suffer from lack of grounding?

The cable is as you describe.

Any thoughts on why 3.5mm out from keyboard directly into 3.5mm jack on monitors or Zoom Livetrak might reduce (but not eliminate) the problem? Perhaps due to your grounding idea?

Again, forgive the complete bafflement...
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Re: Reducing noise from keyboard output?

Postby Sam Spoons » Thu Feb 25, 2021 7:06 pm

A two pin connection doesn't have an earth so adding one somewhere will ground the whole system via the audio connections (the keyboard headphone socket's sleeve connection will almost certainly be connected to the keyboards chassis and screening). It may be that you already have an earth somewhere, more detail about your rig would help. If you have no earth anywhere the system would be more susceptible to picking up interference.

Tell us exactly what you have and how it is connected together and maybe we can help.
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Re: Reducing noise from keyboard output?

Postby ultraGentle » Fri Feb 26, 2021 12:59 am

The whole setup is fairly simple, and is as follows:

All power comes from a 3-pin power strip / surge protector.

All audio equipment is, however, 2-pin.

Casio CDP S350 > 3.5mm headphone out > into the following, with results as noted:

(1) Zoom H4N combo jacks via 3.5mm to dual 1/4" TS --> results in F4 hum. Very hot signal. Need to turn gain down to lowest setting, and still get an audible signal with some hum.
- or -
(2) directly into AudioEngine A5 analog 3.5mm jack --> quieter F4 hum (but audible if turned up way past sensible levels).
- or -
(3) into Zoom LiveTrak L8 3.5mm jack via TRRS (jack originally intended for mix-minus podcasting) --> no hum, but "film reel" noise present.

I wonder if the TRRS aspect of (3) is a clue -- something to do with grounding? Unfortunately I no longer have the unit, though I will soon have a MOTU M4 to test against.

I suspect it is just a low-quality headphone output, but I am open to the possibility that this is solvable, and willing to experiment!
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Re: Reducing noise from keyboard output?

Postby Mike Stranks » Fri Feb 26, 2021 10:21 am

As Sam has said, your first step is to introduce an earth/ground somewhere into your system.

[This is not an esoteric irrelevance. I inadvertently had a ground-free setup on one of my live-sound rigs a while back. You would not believe the 'funnies' and generally sub-standard performance that I experienced. :) ]

The simplest way to do this is to make up a cable with one wire - no earth/ground, nothing. Connect this single wire to the sleeve of a TS/TRS plug and connect it to any spare socket in your recording rig. Connect the other end to a known good earth - ideally your electricity supply via a mains plug. Some of us have used 'Groundology' products for this purpose.

See Hugh's 'Why and How' review here: https://www.soundonsound.com/reviews/groundology-earth-connection-plug

Groundology: https://www.groundology.co.uk/ sell mains plugs to suit most of the main world-wide wiring systems.

Having done this, if it doesn't significantly improve things come back and we'll be pleased to offer further advice.
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Re: Reducing noise from keyboard output?

Postby ultraGentle » Wed Mar 03, 2021 2:58 am

Well, we have progress and mysteries!

The progress:
Following the article above, I used balanced connections from my keyboard to interface (3.5mm to dual 1/4" TS) and then from the balanced outputs to my active monitors (dual 1/4" TS to 3.5mm). This completely stopped the "chatter," and reduced the hum.

The mystery:
With both L and R outputs connected to the interface, the hum still remains at a medium volume, now a C4 with an Ab above, as well. With *only R* plugged in, the hum is gone completely. With only L plugged in to the interface, the hum is present quietly.

Unfortunately, I have zero electrical knowledge, and I wouldn't know how to begin making custom wires. Provided the cost isn't exorbitant, I'm inclined to continue with off-the-shelf solutions.

Given the above, any suggestions on how to proceed? I'm open to purchasing a cheap DI box, but I'm heartened that progress was made simply by connecting to active monitors.

As always, I appreciate the troubleshooting, and I'm willing to learn or be convinced as to the best route!
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Re: Reducing noise from keyboard output?

Postby Sam Spoons » Wed Mar 03, 2021 10:34 am

A couple of points, TRS stereo to 2 x TS and vice versa is unbalanced, I'm guessing that's a typo but for clarity I'll mention it.

Secondly, did you earth the system in some way? If all your equipment has only two pin power connectors, or plastic earth pins then you have no earth, as Mike and I have said this it the first step, anything else that seems to help before you have done this is just coincidental.

There is no point in buying an earth isolator or DI if you have no system earth.
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Re: Reducing noise from keyboard output?

Postby Mike Stranks » Wed Mar 03, 2021 10:36 am

How to make an Earth/Ground connection when you don't want to solder:

https://www.soundonsound.com/forum/view ... 44#p711810

I suspect that your revised arrangements are helping because you have now introduced an earth/ground into your setup.

Your description may be imprecise, but, as written, you haven't actually 'balanced' your signal chain.
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Re: Reducing noise from keyboard output?

Postby ultraGentle » Wed Mar 03, 2021 6:29 pm

Okay, a few atomic Q and A, in an effort to disambiguate:

(1) Sam, sorry, I am confused. In an earlier post:
>> if it is 3.5mm TRS to 2 x ¼" TS you are fine. << Yes, that is what I'm using. So, not fine? (Not being accusatory -- just clarifying.)

(2) If I were to replace the dual TS end with dual TRS, would this then balance the connection? And if so, would it help, given the connection to active monitors?

(3) The system as a whole does have a ground, via the power strip that all the individual 2-pin components are plugged into. Am I correct in understanding that that is *not* sufficient? If it is sufficient, then a DI box should solve the issue (?).

(4) Mike, thanks for the non-solder walkthrough link -- *that* I think I could actually manage! The audio accessories pictured in your post don't seem to be available through Groundology -- would you mind telling me their names so I can purchase them elsewhere?

Step by step...
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Re: Reducing noise from keyboard output?

Postby Sam Spoons » Wed Mar 03, 2021 10:07 pm

Ok, here goes....

If all the power connections to your various pieces of equipment are two pin it doesn't matter that the power strip is earthed since none of the equipment has a connection to that earth. You need to get the system connected to earth by some other means than through the various power connections. Only one of them needs to be earthed but at least one of them must be or you have a 'floating' system which is susceptible to the kind of noises you are trying to eliminate.

A balanced connection has to have two connections for the signal and a separate earth for the shielding, that is for each audio channel*, a stereo signal has two audio channels, left and right each of which need two audio connections plus earth so your 3.5mm minijack stereo connecter only has three connections and can't, without using some kind of two channel unbalanced to balanced box (either a DI for connection to mic inputs or a isolator like the Art Clean Box for line inputs). Both the output on the sending device and the input on the receiving device need to accommodate a balanced connection scheme for it to work (and even then you need the correct cables).

* the multiple earths are normally connected to each other which usually works and it is only if the multiple earth paths cause a sufficiently large loop that problems can occur.
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Re: Reducing noise from keyboard output?

Postby James Perrett » Wed Mar 03, 2021 10:51 pm

ultraGentle wrote:(1) Sam, sorry, I am confused. In an earlier post:
>> if it is 3.5mm TRS to 2 x ¼" TS you are fine. << Yes, that is what I'm using. So, not fine? (Not being accusatory -- just clarifying.)

In case it wasn't clear from Sam's reply, this is the right lead to use for an unbalanced connection. Would a balanced connection be better? Possibly but then possibly not and creating a balanced connection would involve a special custom made cable or a transformer box. It would probably be easier to sort out the rest of your system so that an unbalanced cable worked here.
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Re: Reducing noise from keyboard output?

Postby Mike Stranks » Thu Mar 04, 2021 12:07 am

ultraGentle wrote:
(4) Mike, thanks for the non-solder walkthrough link -- *that* I think I could actually manage! The audio accessories pictured in your post don't seem to be available through Groundology -- would you mind telling me their names so I can purchase them elsewhere?

Step by step...

Just type "Jack plug; screw terminals" into Google...
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