Too much noise

I am copy/pasting my answer from a similar question:

sorry for my late reply, during the Christmas Holidays we have been away

It might be PWM artefacts or just electrical noise pickup. It is particularly bad when using the display.

to make sure if it is the input or the output stage the one that is creating the noise, you can try to load a sinewave generator and check how it sounds. Usually, the sinewave sounds great.

I've tried several power supplies and running from a 9V battery and the noise level is the same.

The power supply is 99% of the times the source or noise, so it is good to check that.

Currently the noise level is such that the pedal is unusable.

Arduino was never conceived for hi-fi audio, it is normal to have some background hiss but not no make it unusable.

Please check how good (or bad) the soundwave sounds and also have a look to the bias points (+2.5, etc). www.electrosmash.com/media/kunena/attach...-troubleshooting.jpg

The board I'm using is the Keyestudio MEGA 2560 R3

We had bad past experiences with Asian Arduino copies, sometimes they have a "cheaper" power supply that injects too much noise everywhere. It would be ideal if you could borrow an official one and see if the problem disappears..