VISUAL ANALYSER - SPECTRUM ANALYSER / OSCILLOSCOPE / SIGNAL GENERATOR
It's great for fault finding along the signal path or testing transistors. example: If two transistors look identical on the scope and spectrum analyser, they will almost certainly sound the same.
I'm using iRig on an old laptop as a cheap and dirty interface, with some proper scope probes I picked up for free. If you have multiple inputs, it can be run as a dual scope.
WARNING: iRig is designed for guitar signals, and a laptop is designed for line/microphone input level. You need a proper scope to test at higher voltages.
You will destroy iRig and/or your computer attempting to test high voltages - so don't do it, not to mention potentially electrocuting yourself.
Example: Tone Bender MKIV on the scope. 440hz sine wave, approx 130mv TRMS input signal
