Buzzing when recording my digital piano on my smartphone

[batata004]

Hi,

When I connect the LINE OUT of my piano to my smartphone mic (TRRS) to record me playing the piano everything works fine, but there is a very annoying buzz at the background. The only way I managed to make this buzz to go away is to touch with my bare hands at the same time the GND of the LINE OUT and the smartphone surface at the same time (I discovered this by accident / trial and error).

I tried using my wife smartphone, I tried another cable... and the problem is exactly the same: the buzz always goes away when touching both the smartphone and the GND of the LINE OUT with the bare hands.

So I ask you: how can I simulate this "touching" without really touching the LINE OUT and the smarphone? Maybe using some capacitor in series or in parallel some where (maybe between GND of LINE OUT and signal?)... Unfortunatelly I cant ask a person to keep touching my smartphone while I play the piano to record it... Is there some "hack" circuit that I can build and attach to the cable? I have basic electronics knowledge and I am confortable soldering capacitors, resistors... so if you tell me to solder something I can do that!

I recorded a video so you can see this weird behaviour happening:

New video by Gil

photos.app.goo.gl

NOTE: I know that mic level voltage is not the same as line level, however I know many smartphones accept line level at the sleeve of the TRRS including mine smartphone. So using line level at the sleeve of TRRS is not the problem here, also because the recording is really really good when I am touching the GND of LINE OUT and the smartphone.

 

[Holmz]

If you have a DMM (Digital Multi Meter), then maybe you can see what the impedance is between the two.

And in the video, it looks like the cable is not shoved all the way in?

Maybe just put an alligator clip on a wire and attach it to the 3mm jack’s shell, and the other end to the case, or attach it to some foil and put the case on the foil.
Or see if a USB plugged in and charging the phone, helps to ground it?

 

[batata004]

@Holmz Thank you for all your attention! I have a DMM but I just wanna make sure what you asked me to do: do you want me to put the DMM in the RESISTOR mode (DIRECT CURRENT) and measure the resistance between the GND of LINE OUT and the case of the smartphone?

Regarding what you said about the connector was not shoved all the way in, it's a big connector but I assure you it's shoved the maximum I can push it.

I dont have a smartphone USB cable to connect it to the power outlet, tomorrow I will do that and test what you said but I think using the outlet will just introduce more noise... I think using the battery of the smartphone is the safest way to make sure I am eliminiating any potential noise!

 

[Holmz]

@Holmz Thank you for all your attention! I have a DMM but I just wanna make sure what you asked me to do: do you want me to put the DMM in the RESISTOR mode (DIRECT CURRENT) and measure the resistance between the GND of LINE OUT and the case of the smartphone?
…

^Correct.^
See if that work for you.

 

[solderdude]

One thing to keep in mind is that a smartphone from Apple and any other brand have different ground and mic inputs.

When using an apple with a signal splitter cable for android (or the other way around) one might end up with the ground wire being the 'mic' input and the mic input being 'shield' and thus pick up hum like crazy.

 

[mSpot]

As @Holmz mentioned, in your video it looks like the TRRS plug was not pushed in all the way. This is the first thing you should check.

I connect the LINE OUT of my piano to my smartphone mic (TRRS)

These are connections for TRRS on the phone.

At the other end of your cable that plugs into the piano line-out, use the continuity tester on your DMM to verify exactly what lines are connected to the TRRS plug. Line-out ground should be connected to the TRRS ground, and line-out +signal should be connected to TRRS microphone.

 

[solderdude]

As can be seen there is a substantial difference in mic/ground between apple (CTIA) and android (OMTP) phones.
This means it matters what cable is used (how the mic is wired) when using a 3.5mm TRRS cables.
In this case there are 2 fundamentally different connections using the same physical plug without this being clearly shown on the cable/plug itself.

 

[mSpot]

As can be seen there is a substantial difference in mic/ground between apple (CTIA) and android (OMTP) phones.

Some older Android did use OMTP, but phone makers including Samsung adopted CTIA as their standard long ago (at least 8 years). I still have Samsung earbuds with mic that originally came with a Galaxy S7 and I've used it on my MacBook Pro and iPads on Zoom calls.

TS/TRS/TRRS/TRRRS: Combating the misconnection epidemic by Allan Tépper - ProVideo Coalition

There are at least four different varieties of 3.5 mm plugs and jacks, each with its own purpose and application. In the last 60 days, several friends have had severe problems by not understanding the differences and innocently plugged the inappropriate plug into the jack on their recording...

www.provideocoalition.com

 

[solderdude]

Not my experience... not all android wired headphones are correctly used in apple products and not all apple headphones are correctly identified by all android/laptop hardware.

 

[batata004]

My dear friends,

First of all I appreciate all your kindness and inteligence into this issue. I read everything you said and after trying all the suggestions you said, I managed to solve the problem inverting the MIC and GND in the TRRS connector. In my case, I was using GND as Sleeve and R2 as LINE OUT/MIC. Inverting this, making sleeve as MIC and R2 as GND, solved the problem. In my opinion, this shouldnt be safe because the SLEEVE on many connectors also is connecter to the outter part of the connector (in my case the external/outter part is of metal, so all the external part of the connectir is now carrying the MIC signal... I think it would be better if it was the GND). What amazes me, is that despite using it inverted, the recording would work just fine, except by the noise in the recording that would magically go away when I touch the GND and smartphone.

I thought that using GND as the SLEEVE was the default/standard of Smartphones nowadays, at least that's what I read on Google... but it looks like my smartphone and my wife's smartphone needs the SLEEVE to be the MIC and the R2 to be the GND.

I am embarassed for this simple solution, sorry for taking the time of you guys. I have one final question for you: many of you pointed that I was not inserting my connector all the way inside the smartphone. I double checked, and I was inserting it all the way in both of the smartphones I tried, and indeed a little bit of the connector sticks outside (the sleeve). I took a picture of my connector and I am sending you below, you can see it has 15.32mm. Do you have any idea how many milimeters should have this TRRS type of connector? Maybe is mine a little bit too long?

 

[Holmz]

My dear friends,

…

I am embarassed for this simple solution, sorry for taking the time of you guys. …

I… :

• am sort of proud of your efforts fixing it.
• learned something I did not know or expect to find out

Muito bem!