MIDI out & line/in-out audio hum, noise

[Choppin]

@Tmdj

 

I use unbalanced cables from the PX going into a balanced input and it's generally noise free.  The out from the PX is -10 dBV and my recording equipment is set to +4 dBu - because the level is just too low from the Px. However, when I'm not playing the PX and there's supposed to be silence, the vu meters are moving ever so slightly up and down - so there's some noise or other signal coming in - but I can't hear it - even with headphones.

 

 

If you can, you may have to match the PXs line out -10 to your sound card input at -10 .  That may eliminate the noise.  your sound card might default to +4 dBu (professional grade) and it doesn't like not matching the output from the PX.  Or, perhaps the opposite, and you can turn down the volume on the Px.

 

But also, my sound card goes through the expansion slot (not a laptop) and not the USB and it has no MIDI.  I run MIDI through another separate soundcard. 

 

The main point - try checking and matching the input line levels if your sound card allows it to be adjusted.

[David X]

On 12/1/2015 at 6:39 PM, Tmdj.alby said:

Hi! First of all sorry for my bad english, I'm from Italy and I am a new user of the PX5s and the forum.

I had some trouble when using my usb soundcard with pc and the privia.

I want to use the internal sounds of the px5s in conjunction with a vst instrument from computer.

The USB soundcard is able to mix both sources: the external sound (from line-out of the privia) and the signal generated by the pc.

I connected the midi-out of keyboard with midi-in of the soundcard (to control the vst) and the line-out of keyboard with line-in of the soundcard. With this setup there is a high pitched whining noise coming from audio input, that vanish only when I unplug the MIDI cable.

I know that there are some older post about this argument, labeled as "USB ground loop" but I have two consideration about:

 

1) if I plug midi (via USB out of privia) and line to pc directly (without external soundcard) the problem persists.

 

2) If I use another keyboard (an old Roland) with exactly the same setup (with the USB soundcard), there is no noise and no humming at all!!

 

What can I do?

 

Is the Roland MIDI better shielded?

 

In any case, how can I get rid of this problem?

 

Thanks to all for the attention!

 

Bye!

hi, may i know how did you solve the noise problem?

Ciao, posso sapere come hai risolto il problema?

[Jokeyman123]

I suspect some of these issues-in addition to everything else that has been described as the possible problem source-may be that some of the newer keyboards and other equipment in the audio/usb chain, since relying so much on plastic cabinets and smaller IC boards-there are no "groundplains" built into most of this newer plastic construction. Just a guess-based upon so many teardowns I've done-older mixers, keyboards, recorders etc. not only were made with alot of steel-these steel frame assemblies were also being used as groundplains for all this high frequency CPU driven equipment-plus the midi din connections were specified with noise-isolating opto-isolators for precisely this reason-to avoid ground loop noise. Opto-isolators are a special type of "op-amp" that have no electrical connection to pass data-it uses an optical signal in the chip effectively isolating any electrical interference mixing in with your midi data. Look at this, then figure out why you are having problems with audio and usb midi! Some newer equipment doesn't have any of this circuitry! 

 

https://www.midi.org/specifications-old/item/midi-din-electrical-specification

 

If you've done electronics troubleshooting of music instruments-when checking components, most older equipment is using the entire chassis as a groundplain and shield from external and internal ground hum as well as being the negative polarity for all your DC components and boards. Even my little Yamaha QY's have a huge copper groundplain soldered to the IC boards inside.  if you connect a record turntable to a stereo system with a magnetic (very sensitive to ground hum) needle cartridge-you connect the turntable ground wire to a separate stereo metal chassis component or some other electrical ground, otherwise there will be an unbearable hum. Unfortunately as many of you are discovering-this lack of electrical groundplains-some laptops have this internally or as part of the case, some don't-is creating alot of grief when hooking up multiple devices-many of which will not have any such grounding at all. There is no easy solution AFAIK-but I have used 3-conductor TR patch cables (1/4") if your jacks match, for audio which some of these USB/audio interfaces lack-when I've discovered that a standard 2-conductor patch cable-like a guitar or audio cable-is causing hum. Just caught this problem in a Zoom MRS 1266 1/4" input from a keyboard-not Casio-when I switched to a 3-conductor patch cord, the hum disappeared. Even if the jacks are standard 2-conductor, this might solve this problem, depending on what you are connecting to what! But then I had no USB connections going on at all. As far as usb audio that uses the usb connector to pass through audio, unless you can somehow completely isolate the ground loop in the usb connection.....