Can REW be used to measure clipping?

[AustinJerry]

I am involved in a discussion WRT determining the correct output voltage setting for a processor. The recommendation is to experiment with various settings and observe when the output is clipping. I don't have an oscilloscope, and would prefer not to spend the money to buy one. Can REW measure the pre-out signal to determine when there is clipping? If yes, is there a discussion of how one might do this? Thanks for any direction.

 

[John Mulcahy]

REW has a scope, but you'll need to be careful to make sure the soundcard input isn't where clipping is happening - the pre out may well have a greater voltage range than the soundcard input. To get around that you would need an attenuator at the soundcard input, using a pair of resistors or a potentiometer.

 

[AustinJerry]

Thank you, John, I'll give it a try.

 

[peter08]

I may also want to do this, so question: do we detect the clipping by running a pure sine wave and visually checking for when the peak starts to flatten? Or should we check for distortion artifacts on a FR plot?

Also, what sort of frequency would you choose - the default 1kHz or something else?

I also plan to compare the onset of clipping in a couple of power amps (using a 300W resistor bank), and my inclination was to select a low frequency sine wave for that test (maybe 40Hz, instead of 1kHz), based on "gut feel" that a power amp is more stressed driving low frequencies. But then, power calculated from a voltage sine wave does not depend on frequency, so maybe any frequency sine will do.

 

[John Mulcahy]

If the system being tested has any EQ gain then best checking at the frequency where gain is maximum. Another way to check is to use the RTA and look for the odd harmonics coming up as clipping occurs, the transition is usually quite distinct as level increases. A stepped level test could be used as well, using the THD limit option to stop the test when distortion gets too high.

 

[Foundation]

I'm interested to follow your experience with this Jerry. I'd love to understand my own signal chain better.

 

[blekenbleu]

An XY capability for Scope would be handy for checking clipping as well as other nonlinearities, delays etc.

 

[vsaudi]

Hey Guys. Did this work for you? I have some signal issues which may be caused by clipping.

 

[tonescout]

REW has a scope, but you'll need to be careful to make sure the soundcard input isn't where clipping is happening - the pre out may well have a greater voltage range than the soundcard input. To get around that you would need an attenuator at the soundcard input, using a pair of resistors or a potentiometer.

On the subject of using the Oscilloscope function, I have an audio interface Behringer U-Control UCA202 and have been using this sucessfully in some applications where my signal is not too large. However I want to use the RTA function to see if I can deduce the source of hum from an old valve amplifier. I want to put the signal onto the grid of the valves in question to see if I can find where the hum is entering, BUT I am aware that there are some high voltages inside, and I want to know if there is any standard or well established way of protecting the 'probe' and audio interface, like a conventional scope with a very high impedance. I would also like to the see the ripple on the smoothing caps etc but there is a very high DC voltage here.

Any experience/ideas?

I am not about to try any of this until I understand a lot more :-)

 

[DanDan]

SignalScope by FaberAcoustical