Author Topic: Wah Wah DSP help  (Read 2223 times)


Wah Wah DSP help
« on: April 04, 2021, 01:39:02 PM »
Hi everyone, I wanna build a wah pedal, with a DSP. Let the guitar signal in, process the signal with a filter (driven by a potentiometer), and then let the signal out. Would you have a cheap DSP to recommend? If so, programmable in C ++. Thank you very much, I am a beginner. ;D ;D ;D


Re: Wah Wah DSP help
« Reply #1 on: April 07, 2021, 10:40:57 AM »

Your best bet is look for a DSP evaluation board at like which has AD/DA capabilities. You will need some gain on the input to get the guitar signal high enough to take advantage of the AD input signal. You will also need to attenuate the output signal back down to reasonable levels.

Most of the free compilers are C, some C++ either way it would have some basic input output source available. TI and Analog probably have the most DSP's available. Microchip has some 16 bit units. Plus I would also look at 32bit MCU's as they have some good capabilities. I use the Microchip PIC32MX and MZ processors a lot for basic filtering with AD/DA and they work great. You can also look at XMOS which is an IO processor, meaning it has no fixed IO, no I2S which is required for AD/DA conversion, but it has building blocks to make I2S and other protocols. It's a pretty powerful processor to do DSP stuff.

Wavelength Audio, ltd.


Re: Wah Wah DSP help
« Reply #2 on: April 07, 2021, 11:58:31 AM »
For a Wah, you simply need an appropriately designed bandpass filter with sweepable frequency center. This requires re-calculating the filter coefficients in real time as you modulate the expression pedal.

As for guitar audio DSP, the Teensy series of Arduino compatible boards are prefect for learning guitar effects as all the hardword of moving realtime audio around is handled by the Teensy Audio Library.

In order to properly feed analog audio in and out of a digital processor you need a CODEC or at least a decent ADC/DAC that is 16-bit cable. You are usually best off going with a CODEC as it is designed for audio purposes. If you want to be able to use your effect with different pickup types (passive vs active), other guitar pedals in front of or after it (pedals run off 9V) you will need a fair bit of complicated electronics to have a high impedance preamp, the necessary gain (or attentuation) to match the ADC/CODEC input levels and generally protect the circuits from those 9V pedals.

I actually make a hobby board available on Tindie (the Teensy Guitar Audio Pro) for people that don't want to deal with SMD parts and PCB manufacturing themselves, at least not to start, and focus on learning to develop effects first. The schematic is freely available in the documentation in case you want to attempt building your own. Be warned, getting something that basically works isn't too tough, getting something to work well (low noise, proper supply filtering to prevent digital inteference) is far more difficult.

Blackaddr Audio
Digital Modelling Enthusiast