Hey, I'm trying to create an auto wah effect. I've been reading that an auto wah consist of a bandpass filter where one of the options would let the center frequency be controlled by a LFO.

I've tried this, but I'm not sure if I did it right.

So I would like to hear if anyone could take a look and give me some feedback, or share some experiences or have other ways of doing this.

I've attached my puredata patch

Thanks

http://www.pdpatchrepo.info/hurleur/autowahattempt.pd

Hey dingenot,

you had the right idea but your frequency input into [vcf~] was a bit off. A lot of this stuff is all about getting the scaling correct. Sometimes it's helpful to use:

[env~]
|
[dbtorms]
|
[ \

To analyse what's coming out of a signal object.

In your patch, what you called the Center Frequency was actually setting the frequency of the LFO controlling the Center Frequency. I can understand why you used [abs~] to make it unipolar but this will actually double your frequency and also change the shape of the LFO. The reason why you wasn't hearing anything is because the output of your LFO was only going from 0 to 1, thus setting the bandpass filter so low as to be inaudible.

Autowah effects tend to sound good around the frequency of the human voice, say roughly 700 Hz. We also want to set a range for the frequency so that we can actually hear the sweep. If our LFO is going from 0 - 1, then multiplying it by 1000 will make it go from 0 - 1000. Now we don't actually want it to go that low (otherwise we won't be able to hear it) so we can add an offset of say 300 to make the LFO sweep from 300 - 1300.

Check out the attached patch, which shows this in action. I've also added a triangle shaped LFO so you can hear the difference in the sweep. Maybe try seeing what other LFO shapes sound good.

Cheers,
Joe

http://www.pdpatchrepo.info/hurleur/autowahattempt-2.pd

I'd also like to add that the autowah effect is very dependent on its input source. Using a single oscillator like you did would mean you'll probably only hear the input being faded in and out and not the characteristic sweep sound. I used a [noise~] object but try it with a guitar or vocals.

Yop,

William brent's TimbreId examples have an autowah patch :
http://williambrent.conflations.com/pages/research.html#timbreID

Nau

Jwif, thanks a lot for the nice feedback and explanation, that was really helpful and educational! The sweep in your patch is really clear
I have planned to play my bassguitar through this kind of patch to see what happens, but I just need to get my hands on a jack to mini jack converter first

Nau, that sounds interesting, I might check it out

Do you have an audio interface? I wouldn't plug your bass directly into the line input of your computer (it sounds like this is what you're intending to do).

Your best bet is to use a device that has an instrument input (usually called DI). Then in Pd you can set the input to be from said device.

If you get it working, try putting an [env~] object on the bass input and use it to set the frequency instead of the LFO for a envelope-filter

I was actually planning on plugging it directly to the line input and use [adc~]. Would that be a bad idea?

How much do you think a suitable DI would cost? I was planning on not to spend too much money at the moment

Ah great idea, that would be interesting to try! I also read about that one I think I will give it a go sometime, when I tried out the input.

It will work and won't damage anything but maybe read up on the difference between line, instrument and mic levels. Line level is what, for example, a CD player would output, has the strongest signal and can go straight into a power amp. Mic level has a very weak signal and needs a pre-amp to boost it up. Instrument level is somewhere inbetween e.g. bass/keyboards. It might possibly work depending on your bass (if it's active or not) but you'll probably have increase your gain to get it loud enough and that'll increase your noise floor.

You can get DI boxes for guitars and they usually lower your input signal to mic level, but then you'll still need to get that into your PC. Getting a cheap audio interface might be a solution as then you'll be able to cater for different inputs and a dedicated interface is generally much better than the in-built ones.

Take a look at the back of this Mbox http://media.soundonsound.com/sos/nov05/images/digidesignmbox22.l.jpg - you can see it has two inputs each which accept either Line, DI (instrument), or Mic signals.

Okay, I will try and read something about line, instrument and mic levels, to get a better understanding of this.
I have an active and a passive bass so I will try them both and see what the difference is.

Will I have to multiply my input signal to adjust the gain or how is this done?

I will keep my eyes on the DI boxes, but I think I will try and hear what it sounds like when I plug it directly first if its a total mess I will check out the DI box solution

Once again, thanks a lot for your help! I really appreciate it.