Effect Frequnecy Response Testing...

**grygrx** · #1 06-15-2009, 07:15 AM

So I've been thinking about this and really don't know where to start.

I know there are ways to shoot 'pink' noise into an audio appliance and then generate a visual map the frequency response. I've done a little searching but was wondering if anyone had experience and wanted to share before I dug in

Software?
Hardware?
Skills?

rcubed · #2 06-15-2009, 07:27 AM

Function generator spitting out a frequency or frequency range into the pedal with the output of the pedal going into a oscilloscope. If the oscilloscope is a new one, you can put it on your network and capture screen shots.

cheapbasslovin · #3 06-15-2009, 07:35 AM

Audacity has a 'generate white noise' track. It also has an 'analyze/ plot spectrum' selection that allows you to look at a tracks output. Seems to me if you run the white noise through a pedal and then back into a second track and analyze track two you'd be set. You'll want to tweak with some of the settings on the spectrum analysis to be able to see down to reasonable bass frequency levels, and also tweak with the linear/ log spectrum mapping to decide what you like looking at better.

scotch · #4 06-15-2009, 07:45 AM

I've fiddled with this a few times. I use my Mbox2pro interface to send a pink noise signal into the pedal, then the output of the pedal is plugged back into a recording channel of the interface. I then use Audacity to analyze the clip. I then compare the generated graph of the Pedal" pink noise to a control graph. For the control graph, I used the same exact method, but just ran a 1/4" cable in & out of the interface without a pedal. That way, the interfaces' preamp is factored in...

I prefer the pink noise to white noise as it is better tailored to audio diagnostics.

Mr. Pickles · #5 06-15-2009, 08:08 AM

PM sent.

bongomania · #6 06-15-2009, 09:17 AM

I believe TB'er fdeck has a software app for this purpose. I've been looking into portable spectrum analyzers, but the decent ones are hella expensive. From what I have gleaned so far, looks like software is the only way to fly on a budget, and for portability I'd just need to pick up a PC mini notebook with a good built-in sound card.

Software I've seen recommended:

Audacity
Blue Cat
Voxengo SPAN
RND Inspector
Audiofile Spectre
RME Digicheck
Spectrafoo Complete
Waves PAZ

Of those, seems like Audacity, Inspector, and Spectrafoo get the most props.

**grygrx** · #7 06-15-2009, 09:32 AM

Quote:

Originally Posted by bongomania

I believe TB'er fdeck has a software app for this purpose. I've been looking into portable spectrum analyzers, but the decent ones are hella expensive. From what I have gleaned so far, looks like software is the only way to fly on a budget, and for portability I'd just need to pick up a PC mini notebook with a good built-in sound card.

Software I've seen recommended:

Audacity
Blue Cat
Voxengo SPAN
RND Inspector
Audiofile Spectre
RME Digicheck
Spectrafoo Complete
Waves PAZ

Of those, seems like Audacity, Inspector, and Spectrafoo get the most props.

Curious about " hella expensive " items, and specifics ones you've looked at and general cost ranges? As I have no children, I tend to waste the money on my toys instead of theirs

Funk&Disorderly · #8 06-15-2009, 09:48 AM

I like this idea, even though i am a lay person when it comes to acoustics.

I'll be very interested to hear some of your findings.

Subscribe-o-rama.

bongomania · #9 06-15-2009, 10:32 AM

The handheld analyzers are mostly in the $4K to $10K range.

Also the vast majority of them are designed for ultrahigh frequencies, not audio range, so that's part of the "search" as well. So far I have only found one handheld audio-range analyzer under $4K, and it's only $400, the Phonic PAA3:
http://www.phonic.com/en/testers/paa3.html
Problem is, it only has a 31-band resolution across 20Hz - 20KHz, so there's not a lot of information to see about low-end rolloff.

dannybuoy · #10 06-15-2009, 10:49 AM

I've used FDeck's software to measure the response of the VT Bass in this thread:

VT Bass frequency response plots

All I used was my laptop with built in sound, I couldn't get it to work with my fancy firewire audio interface!

niftydog · #11 06-15-2009, 05:26 PM

Sure, it's nice to have a fancy plot, but if all you want to do is find the bandwidth this can be done with an audio frequency generator and an oscilloscope.

First you find the rough average in the middle of the band just by dialling the generator between around 300hz and 3khz - this should give you an idea of the voltage amplitude in the flat portion of the imaginary spectrum plot.
Then you calculate what voltage correlates to -3dB and wind the generator down/up until the pedal output reduces to that voltage. Measure the frequency at those points and there's your bandwidth.