Amplitude sweep stimulus/probe

Hello,

I'm afraid that the Stimulus / Probe modules can only plot the frequency response of what's between them, with additional limitations. If you have your hardware or an evaluation board handy, however, you can make a project to plot this amplitude response without using any external test gear. An example project is shown below:

The attached project applies a 100 dB amplitude range (-80 -- +20) to the compressor under test. It runs on a ADAU1701, yet this idea is easily adaptable to any DSP.

Best regards,

Bob

Plot-Amplitude.zip

Hello dunmail,

The post and the project that Bob gave is excellent and you certainly can measure the release times and characteristics of the curve but it is not useful for measuring the attack times. The Graphing function is a readback that happens I believe every 10ms and then it graphs the points that it reads. So any attack time less than that is missed or it is not quite shown correctly.

The only real way to measure attack is with a good old fashioned oscilloscope! Send the output to a DAC and look at it on a scope. You should also send out a trigger signal on a GPIO. Just put a "T" on the trigger signal, put in a hardclip to make the output be zero and 1 instead of -1 and 1, and send it to a GPIO.

That will make it easier to capture the attack with a single sweep.

Dave T

Thanks for the suggestions guys. I'm not so worried about attack/decay, like you say I can check that with a 'scope, it's more a rapid & simple way of checking arbitrary amplitude responses. One small problem though, I can't find the log10 function in arithmetic operations on the ADAU1787 - can you think of any way round this please?

Hello dunmail,

The -1787 sure is an interesting chip. Not only does it include the fast DSP for use in noise-cancelling headphones and such, but its slow DSP features hardware accelerators for common math functions. You can read more about this HW acceleration here. Thus, the log function is located in a group separate from the arithmetic functions, as shown below. Since only the natural log function is included, convert it to common log as shown.

Because of my curiosity about all these math functions, I obtained a -1787 eval board. However, I have found both its user manual and the -1787 data sheet too confusing for me, so I have not done anything with the board. If you happen to have a simple project which puts audio through both DSPs, please share it.

Best regards,

Bob

Thanks Bob, I'd assumed it would be in with the arithmetic functions. Unfortunately I'm working under an NDA for this project, but if I come with anything else that uses both cores I'll post it up here. It's a very useful chip this, it's just a shame the FDEC/FINT don't allow the use of some of the sampling frequencies.

OK so I've set up a ramped amplitude generator (left out the compressor for now - don't try to run before you walk) and graphing thing, but as soon as I try to plot the output I get this error from Windoze:

Anybody got any ideas as to a way round this please?