How to measure frequency response with a PC?

[zafira1981]

Hi people,

I'm trying to measure the F.R. of my tube amp (Help modifiying schematic) and I cant make TrueRTA work.

I tried with NVIDIA SoundStorm sound card an Sound Blaster Audigy 2 ZS. I cant calibrate the sound card to have a plain frequency response to start measurements.

I don't know what is my mistake.

Sound Controls (both cards tested):
recording: line input selected, at MAXIUM
playback: wave and master at maxium, line input muted (To avoid oscillations)
Loop cable conected between line in and line out.
I also checked and no "audio effect" is ON.

Any clue? Any other program to use?

[Gold_xyz]

Hi

Try an oscilloscope/spectrum analyzer from this site
http://digilander.libero.it/hsoft/

Link download : http://digilander.libero.it/hsoft/VA.zip
(with continous spectrum )

[TugaTweaker]

This can be useful too .

http://www.usb-instruments.com/oscillo_stingray.html

[zafira1981]

Originally posted by Gold_xyz
Hi

Try an oscilloscope/spectrum analyzer from this site
http://digilander.libero.it/hsoft/

Link download : http://digilander.libero.it/hsoft/VA.zip
(with continous spectrum )

Thanks for your reply!!!!

I've downloaded the program. I'm trying to calibrate it. Wave generator is configured as Sweep. After a few loops, the graph shows the frequency response of the sound card:



Is there any way to "flat" it to correct the response of the sound card?

thanks
Jorge.

[KimBOlesen]

Hi

try this -> http://audio.rightmark.org/products/rmaa.shtml with this program you can subtract the soundcard data from your amp's data.

Best regards Kim Olesen

[zafira1981]

Originally posted by KimBOlesen
Hi

try this -> http://audio.rightmark.org/products/rmaa.shtml with this program you can subtract the soundcard data from your amp's data.

Best regards Kim Olesen

Wowww that program seems to be really nice!! thanks!! I will try it. thanks!!!!

Jorge.

[Svein_B]

I often use ARTA, the speaker measurement program also for amplifier measurements.

- The Spectrum analyser is nice for measuring harmonic distortion, and it has built in tone generators.
- Compensation files can be loaded.
- FR measurement is OK, but most PC's fall short here with a limit of 20KHz. The same can be said for usefulness of any soundcard based oscilloscope.


Svein B.

[Conrad Hoffman]

Zafira, I like VA quite a lot. If your sound card can sample higher than 44.1khz, you can test higher than 20khz. My inexpensive E-mu 0202 USB box supposedly can go to 192khz, though I haven't pushed it that far. Tests at 40khz (96khz sample) and more seem fine. I notice that your level is -60 db in the graph you attached. That's way down there- check your levels and 0dB setting. You might also find it interesting to use the pink noise source and set the analyzer for 1/3 octave or finer measurements. Handy when you move beyond the amp to the speakers.

[nhuwar]

As far as hardware goes iIve been eyeballing this. ! channel o scope 400hz to 16 mhz spectrum analyzer.

http://www.velleman.be/ot/en/product/view/?id=348712

Nick

[kevinkr]

I believe if you are using line in and out and doing a loop back test the line input needs to be unmuted - that is where the signal you are trying to measure is connected to.

There should be no oscillations with loopback connection and both input and outputs enabled.

Note that depending on level settings and sound card you may clip either the input or output, this should be fairly obvious if you get high thd numbers.. I generally run at no more than 90% of digital FS to get good results.

I use Arta and Audio Tester.