[sdiy] Dry/Wet effect relay that makes 'click' noise on changes...

[Tom Wiltshire]

On 11 Jan 2016, at 11:18, Mattias Rickardsson <mr at analogue.org> wrote:

> On 11 January 2016 at 11:44,  <rsdio at audiobanshee.com> wrote:
>> Rather than a fairly complicated and expensive circuit like a sweepable filter, why not just fades from full volume to mute?
> 
> Because the long time needed for gently fading bass frequencies is too
> long for the higher frequencies if they need to be perceived as
> starting or stopping immediately. :-)


In practice, this isn't such an issue as it might appear, at least for stomp box use. The lowest note on a guitar is 80Hz, iirc. That's a 12.5msec period. Fading it in or out over 10-20msecs avoids a click, and is fast enough to be imperceptible. After all, you don't know exactly when the switch is going to engage, so there's no perception of a delay ("I pressed it, I waited, then it came on"). Instead, you perceive it as having happened when it comes on, even if the switch actually engaged a moment sooner.

A slow-fade is exactly what the Boss FET switching does. For example, the CE-2 chorus pedal uses a 1M and 47n LPF on the signal coming from the bistable to slow the rise/fall time and make a soft fade in/out. That's a rise time of over a second, but the FET's response won't be that linear, so the overall effect isn't of a 1 second fade in.

Tom