[sdiy] Tap tempo question

Richie Burnett rburnett at richieburnett.co.uk
Tue Feb 2 13:03:16 CET 2021


I don't know what the algorithm is in my Roland TR-8 drum machine here, but 
it definitely does some sort of averaging.  If you change the speed of your 
taps it pushes or drags the tempo of the pattern that's playing.  It doesn't 
immediately sync each beat to the new tap instants (because that would cause 
a glitch in the drum pattern) but it does eventually sync up if you keep 
tapping at a fixed speed.  Someone has obviously given it some thought, 
because whatever it is doing inside the box feels very intuitive to the 
user.

It feels like the tempo jumps to the new tap tempo after 3 taps.  And then 
the "phase" adjusts gradually after that until the pattern is eventually in 
sync with the taps.  Maybe it uses some sort of software phase-locked-loop.

-Richie,



-----Original Message----- 
From: Tom Wiltshire
Sent: Tuesday, February 2, 2021 10:59 AM
To: Markus
Cc: SYNTH DIY
Subject: Re: [sdiy] Tap tempo question

I am on the list.

I don’t think there’s a “more sensible” or “accepted” way to do it. It 
depends on the purpose.

Averaging makes some sense where you’ve got a human tapping, and Brian is 
right that weighted averages are a good idea to give more recent times more 
importance. Rather than doing hard sums, on a PIC it makes sense to do this 
weighting by using bit shifts (so choose from weights of 1, 0.5, 0.25, or 
0.125!!).

However, if you’re likely to use the tap tempo input for syncing the delay 
to incoming tempos from a drum machine or sequencer or similar, then just 
measuring the last two pulses and using those only makes the thing much more 
responsive. You don’t need to worry for a delay, but for my tap tempo LFOs, 
I also needed to think about the phase, and it’s important to reset or 
adjust the phase so that the LFO waveform is on the beat, not just in time.


==================
       Electric Druid
Synth & Stompbox DIY
==================




On 2 Feb 2021, at 00:43, Markus via Synth-diy <synth-diy at synth-diy.org> 
wrote:



sounds like Tom Wiltshire from Electric Druid would be the expert on this. 
is he on this list?

https://electricdruid.net/electric-druid-chips-the-next-generation/

On Monday, February 1, 2021, 04:40:12 PM PST, Didier Leplae via Synth-diy 
<synth-diy at synth-diy.org> wrote:


I am currently working on a delay module using a PIC uC to control the delay 
time so adding in a tap function.
Thus far, I have the PIC measuring the time between two consecutive taps to 
determine the delay time. But it occurred to me that sometimes when I use a 
tap tempo, I tap multiple times with the assumption that the multiple taps 
are averaged.
Does anyone have an opinion on which is the more sensible or accepted way to 
do this?
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