Audio problems: High freq. hum & USB

[Hapbarb]

Hi!
I'm running my Prophet X through an Apogee Duet (all current firmware and software) into Logic Pro X on a mid-2012 MacBook Pro.
Hearing a high frequency hum (about 600) through my monitors.
Also, audio stops when USB is connected. I went through all sorts of 9to5 Mac steps to set up my PX as an external instrument; note info shows, as well as track input levels, but still no audio out.
1/4" outs work fine - as long as USB is disconnected.
I'm ready for good advice.

[Steve in VA]

I've experienced noise with long USB cables with other devices. Interestingly, my last keyboard came with some kind of a clamped coil to put on the USB cable to prevent noise. I did not need it in that case, but perhaps this might provide a clue for you.

[Hapbarb]

Thanks, Steve. I may not have been clear; I only get signal at ALL when USB is disconnected. I think I'm going to have to call Sequential tech support.

[extreme measures]

I have the same problem when USB is connected. It's a ground loop?.
On any computer system.


Please post here if you find a solution.

[Robot Heart]

It does sound like a ground loop from your description. See my answer here:

https://forum.sequential.com/index.php/topic,2629.msg28837.html#msg28837

[catman]

Hi!
I'm running my Prophet X through an Apogee Duet (all current firmware and software) into Logic Pro X on a mid-2012 MacBook Pro.

I've found MacBook Pros can have a lot of noise on their USB lines.  I have a Mackie Big Knob that has a USB port for audio.  The USB port allows you to use the Big Knob as an audio interface.  The Big Knob is connected to my monitors.  I found that if the USB port from the MBP is connected I got noise out of the monitors.  If I unplugged the USB port - no noise.  I purchased this on Amazon and it filtered the noise right out https://www.amazon.com/gp/product/B01N3XKOLG/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1.  It would seem that the Big Knob doesn't isolate the USB from the audio paths at all.

That might be the case for the Prophet X.  The USB connection going into the Prophet X is plugging into basically a computer motherboard (which also connects to the audio boards).  It might not have isolation between the digital side and the audio side or you might be transmitting noise from the Prophet X back to your MBP and then into your Apogee.  There are lots of paths noise can take so you'd have to play around a bit to find where exactly the noise is coming from.

It might be something to consider...

[catman]

I went through all sorts of 9to5 Mac steps to set up my PX as an external instrument; note info shows, as well as track input levels, but still no audio out.
1/4" outs work fine - as long as USB is disconnected.

I hope your aren't trying to get audio out of the USB connection.  The USB connection is for MIDI only, it is not an audio interface.  You'll get your audio out the 1/4" ports.  How are you triggering notes?  From the keyboard, MIDI, or USB MIDI?  The notes could possibly stop when the USB is connected if MIDI local is off or something like that.  You can set the Prophet X to use the USB port or the MIDI port for USB in/out.  I don't have the manual in front of me, but you might want to look at your MIDI settings in the GLOBALs.

But don't expect to get audio out via the USB port.

Best regards,
Lenny

[tommym]

Thanks, Steve. I may not have been clear; I only get signal at ALL when USB is disconnected. I think I'm going to have to call Sequential tech support.

I find that turning the Prophet X's Master Volume down, sends that command over Midi too. A bit unconventional. By the same token, if, after plugging in USB and immediately losing Audio volume on your PX, if you were to turn its Volume knob down and then up again, does the sound return? Sorry if that's the first thing you tried already!

I am also experiencing USB Ground Hum, so I am going to look into the various solutions mentioned above. Thanks!

[extreme measures]

As an audio engineer and synth developer of some 40 years, I do understand groundloops and studio wiring pretty well. But the X is the only device in my entire rig that will generate massive hum when plugged in when audio AND USB is attached to the Intel Mac Pro running the room .

[tommym]

Thanks, Steve. I may not have been clear; I only get signal at ALL when USB is disconnected. I think I'm going to have to call Sequential tech support.

This may be related, because USB passes MIDI - When I connect a USB cable between my MBP 2015 and the Prophet X, latest firmware version, and *arm a Midi Track to Record in Digital Performer* - audio stops coming out of the Prophet X's 1/4 outputs. When I re-click the little red Record button on the Midi Track, the audio comes back on.

Note, I don't have to start Recording (the transport doesn't have to move.) Nope, the instant that the track is 'armed' to record, the Prophet X's audio disappears. When I click a 2nd time on the track's 'record-ready' button, the audio from the synth returns.