you could set up the recording trig to replace a sample at every pass of the record trig - or you could use a one shot record trig and occasionally re-arm - or just manually record to that buffer as shown
i really like the concept of using one live capture across all tracks and resampling, especially with something loose like the monotron
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if you want to run through the ins and outs of sampling it’s time to hit the manual/forum/tutorial vids
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in this instance the recording length, rlen, is probably set very short &or the amp env is shaping the sample