strange behaviour of Ibanez UE405 analog delay

[Gil]

I noticed something strange with the analog delay on the UE405 multieffect. Sometimes it sounds to me like the replica's pitch is slighlty different than the imcoming signal. Additionally, the max delay time (when the delay pot is on max) sometime is just shorter than it usually is.

Is there anything to so with the fact that I "pushed" the BBD over the point where it was originally set ? I actually used the clock trimpot to make the max delay time longer.


Thanks.

[Gil]

bump

[Mark Hammer]

The pitch can only be physically different if there is a fast enough change in sampling rate at some point.  Other than that, you can not physically create a static pitch shift with a single BBD.

On the other hand, it is a known psychacoustic effect that perceived pitch corresponds slightly to volume level.  Listen to a fade out on a recorded song and it will often seem to change pitch slightly as it fades out.  Just the way your ears work.

"Pushing" the max delay time with the trimmer should essentially have only a few predicted effects.  One is obviously extending delay time.  A second would be increasing the audible level of any "motorboating" or clock-bleedthrough by lowering its frequency into a range below the cutoff of the on-board lowpass filters and where the ear is more sensitive to it.  A third would be that the individual storage cells are obliged to hang onto the signal for clock cycles longer than is healthy for the signal with the result that sound quality is quickly degraded. The teeny-weeny caps in each of the BBD "stages" leak, and just like true bucket-brigades, if you keep them moving fast enough they don't lose much, but wait too long before transferring charge and some of it will have leaked.  If you keep your bandwidth very restricted, you don't notice it, but if you are aiming for 3-5khz bandwidth, don't expect to hear it when you max out the delay time.  You can also expect each repeat that recirculates through the chip to be of even less quality at such "under-clocked" delay times.

The erratic nature of the delay time overall is likely a product of a trimpot setting which places the trimpot wiper at a physical location which results in less reliable contact.  If you find the tone is acceptable as such under-clocked delays but wish it were less fickle, change the trimpot for a new one of the same value, if possible get a multiturn trimpot so you can dial in that point just before sonic quality bottoms out.

[zachary vex]

how did the mxr bbd-based pitch shifter work?  the one that had the 4 touch-sensitive knobs on the front?

[Gil]

Thanks a lot Mark,

yeh, it looks like the pitch change is caused by the delay time that is slightly changing through the playing, which results in a fast pitch change,
it actually sounds like there is a chorus is in the loop. Quite interesting sounding...