I need to measure my 48V phantom power mic preamp for linearity and I don't have a clue as to how to do it. I also need to know what to use. I've searched a bit but nothing what I deemed useful showed up. The preamp input uses XLR and TRS (combo input).
This is much, much simpler than people are saying. People measured this kind of stuff way before there were computers and software. Let's go back to the 1950s and ask how would we do this.
Basically you put an AC signal of some frequency into the amp. You measure it's A/C voltage. Then you measure the AC voltage at amp's output. (You need to place a dummy load on the amp's output) Then look at the ratio of the two voltages. Make a dot on some graph paper. Change the frequency and do this again.
If you don't have a sound card and software for making the tomes you can have an iPod that plays test tones from an WAV file. You can download the wav files and burn to CD if you want.
What the software does is automate this process. but if you can make some test tones and measure AC voltages and draw lines on paper you can do this. The accuracy will be limited by the accuracy of your method of measuring AC volts but if you are just looking for a graph that is good to about 1 dB you don't need professional quality test equipment.
There is some advantage of doing this my hand, yougain a better understanding of what you are doing