MOUT M4 NOISE

[DR ANALOGUE]

Has anyone an idea about the acceptable noise of the M4?

Measured directly at the XLR output, I measure around +- 8mV when the device has started up. This does not change when the computer is on battery, the USB externally supplied, or even USB-cable is conneted only by an high quality PSU.

M4NOISE1: USB supplied by high quality PSU, before M4 has compeletly started up
M4NOISE2: USB supplied by high quality PSU, M4 started up


Therefore, I would consider the noise coming from the M4 itself.

Any suggestions?

Many thanks in advance

Michael

 

[Mark Tillotson]

What is MOUT M4? Do you mean MOTU M4?


Noise is measured as rms value with a specified bandwidth, or as a spectral density - can't compare otherwise, its meaningless without the bandwidth.

 

[1audio]

The Picoscope bandwidth is wide enough that you will see a of of out of band noise. if you lower the bandwidth to 100 KHz you will start to get something useful. However the output noise would be measured using A weighting which would eliminate both HF and LF content. I think there may be a way to do that in their software.

Everyone uses a weighting because the results can be compared meaningfully. Still you need to check output gain levels etc. and also be cautious of ground loops and switching supply noise that will degrade the measurements.

 

[DR ANALOGUE]

OK, thanks.
The FFT seems to be OK. I am still wondering about the noise at the output....

Best
Michael

 

[phofman]

Please try a different frequency than 1kHz, to see what is harmonics and what is 1kHz USB spurious.

 

[Mark Tillotson]

Can you set the FFT to spectral density? Then you can measure the audio band noise directly.

 

[mlwebb]

I have been looking at my m4 (and learning a little about measurement).
Arta will give a THD and a THD+N number, or you may find what you want poking through the AudioScienceReview thread.

Michael