Why you should test your circuits at high and low sound levels

Bit of a random post from me, as it's been awhile - but I thought it might be interesting for some.   

So back in the day I used to work as a Sound Engineer, and one of the first things I remember learning about was Fletcher-Munson curves (now superseded), also known as equal-loudness curves.  There are other methods as well, but we'll just stick to equal-loudness contours to keep things simple.

These curves attempt to map how our ears respond to different frequencies at different sound pressure levels.  So what does this have to do with making pedals?  Well quite a bit really.

Note the chart below, and the differences across the frequency range at different levels - if you test at low levels, expect some surprises when you turn it up, and of course the opposite applies when turning it down.  You might find the circuit that you thought was missing something at low levels, really hits the spot at stage levels and vice versa.  

Unfortunately I can't find a chart that focuses on the 70 - 120 dB range, as guitars have no business being lower than 70.  If you're unfamiliar with sound measurement, 10dB jumps are very large - 10dB is subjectively considered to be twice as loud.   

Naturally this extends to amps as well, and all things that make noise.  Good Mastering Engineers generally have wizard like skills when it comes to mastering a track that will sound good at different levels - which also explains why some songs only sound good loud.