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I'm looking for a DIY or professional method for easily measuring frequency response of an audio system from 10Hz to 10kHz. It is for a guitar amplifier, and I would like a better way to characterize my changes without playing actual guitar through it all the time as I'm tweaking. Note this is a tube amplifier, so not easy to model.

In the RF world I would use a Vector Analyzer... I was trying to come up with an easy way using a scope and a sweep generator, but have yet to think of a good method. The best I have so far:

  1. Create a DDS system with an Arduino platform and take ADC measurements of the input and output peaks, but that involves a whole project on its own...
  2. Using a DMM on AC mode, but it gets inaccurate above 1kHz it seems. (Faster then reading scope lines)
  3. Some sort of Audacity plugin or program using my PCs audio card? (Nice automated plot or data export?)

I should note my scope does not have auto measure capability, it is from 1978... Otherwise, yes a modern scope I could at least use peak measure as I change the frequency generator.

Currently I occasionally take a pile of hand measurements with a generator and scope. Manually changing the frequency, and writing down the measurements.

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  • \$\begingroup\$ Non-linear effects (=distortion) in a guitar amp and speaker are as essential as the frequency response. Those non-linear effects cleare frequency components that were non-existent in guitar's sound, the amp literally "adds sound" and the speaker adds more. Frequency response measurement need so low volume that non-linearities are not substantial. Speaker is as essential as the amp, so you need an audio analyzer with high cost precision microphone. \$\endgroup\$
    – user136077
    Commented Mar 29, 2020 at 9:52
  • \$\begingroup\$ Speaker effects will not change with pre amp alterations. I am just trying to get baseline measurements for implementing feedback and different tone controls. I don't need crazy stuff like .5dB precision. And I would be taking from the input to the output transformer, so most of the non linearities would be covered. Thanks though for the thought \$\endgroup\$
    – MadHatter
    Commented Mar 29, 2020 at 15:44

2 Answers 2

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Rightmark Audio Analyzer is a free tool for performing frequency and distortion measurements on audio equipment using a sound card (or any recording device that can save PCM).

If your goal is only to measure frequency response, almost any laptop would be sufficient. Hook up the line out from the laptop to the input on your device under test. Then take the output from the DUT to your line in. Set the sample rate you want in Rightmark and hit go. It'll take a few seconds and then give you the transfer function of the device (as well as a lot of other information you may or may not have a use for).

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  • \$\begingroup\$ Thanks, this looks exactly like what I am looking for, since it is a guitar amp, I do not need anything to precise, although this with a good sound card seems like it could be quite nice. \$\endgroup\$
    – MadHatter
    Commented Mar 29, 2020 at 4:42
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A simple way to get the frequency response is to measure the impulse response.

The impulse response is related to the frequency response. The frequency response is just the Fourier transform of the impulse response as described on the DSP pages.

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