Re: Lo Fi Looping

[David Myers <dmgraph@earthlink.net>]

Title: Re: Lo Fi Looping

Thanks Jon.  Interesting, about the record life of these chips--didn't catch that in the spec sheets.  Definitely think that limits the practicality of overdub schemes.  So I definitely will try the simple way, at least at first.

I'd like to try the ISD 1416--16 second memory, and the best bandwidth these things offer, 3.4 kHz. The best price seems to be from nuhorizons.com--but they are out of stock.  Like everyone else!  I hope there isn't a problem with the company.  Digikey lists a backorder to October 7, maybe then we'll see what's happening.  Til then, guess I'll mosey over to Radio Shack and see if they have a piece to play with.

DLM

on 8/29/02 11:52 AM, Jon Wagner at jondrums@hotmail.com wrote:

> > Thanks Jon.  Yes, there seems to be quite a few versions offered by ISD.
> > Where did you purchase your chips?
> good question can't remember, but you can get them here for example:
> http://www.digikey.com/scripts/us/dksus.dll?Criteria?Ref=51278&Cat=30082135
>
> > > The big drawback as I see it is that there
> > > is no provision for overdub or feedback, but you could get this with a two
> > > chip design if you were clever.
> Not that clever, but here's the gist:  You have two ISD chips which both can either record or playback.  There are two states:  A and B.  Lets say you have recorded a loop in ISDchip#1.  In state A, you playback the loop once on ISD1, and record on ISD2. ISD2 takes its input from both the mic, and the output of ISD1 x FEEDBACK.  Then as soon as ISD1 signals its the end of playing the loop, you switch to state B where ISD2 is playing back and ISD1 is recording the mic + ISD2 x FEEDBACK.  Keep going back and forth this way, and you have a basic system with feedback and overdub.  You could put a switch in to enable the overdub function by simply turning the mic on/off.  The feedback could be a potentiometer voltage divider so it is variable.  I'm pretty sure you could do the whole thing in digital logic based on the ISD chips outputs and inputs. 
>  
> Ok, here's the one problem with this scheme - those ISD chips have a finite number of record cycles before they die.  I think its spec'd at 100,000 cycles.  So say you play a 15 second loop for 1 hour each day.  That's a little over 2 years of life before you have to change out the chips.  It all depends on the desired usage.  They don't spec a lifetime on playback, but I would assume its quite a bit many more cycles.
>  
> If I were you I'd attempt your simple system first.  Those chips are pretty straight forward to get up and running with if you read the datasheet carefully.  Good luck and keep us posted.
> Jon