----- Original Message ----- From: Olin Lathrop To: Sent: Tuesday, February 06, 2001 9:24 AM Subject: Re: [EE]: high res DA challenge > > Olin, why is it impossible to guarantee response time or design a > > filter for that? Could you please explain in more detail? > > The way I understood it, you were dithering the input signal with a random > number, meaning white noise in signal processing terms. If your random > number generator is really good, then each output value has no correlation > to any prevous output values and has an equal probability of being anywhere > in the output range. This means it contains all frequencies (up to what can > be represented by the sample rate) equally. In other words, you are > dithering with a signal that contains 1Hz, .1Hz, .01Hz, etc. > > Let's look at this in the time domain instead of frequency. Assume your > desired duty cycle is 50% and your random numbers range from 0 to 1. There > is no guarantee how long a continuous string of random numbers might be > below 1/2. It gets increasingly unlikely for longer strings, but there is > no guaranteed upper limit. Actually, there is a guarantee of the longest possible string of 0/1 - implied by the width of the PRNG. But it is long enough to not be any real help here! Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads