Hi All, If you have a sound card sampling at 48khz with no anti-aliasing filter, and you have a tone spurious or otherwise coming into that card at 38khz the sampled data will have a tone at 10khz in its output that did NOT EXIST at its input.
Thus the name aliasing. It is MUCH simpler and cheaper to have the audio chip provide anti-aliasing than to build multipole L-C filters!! Thus my comment about ISA cards being useful because they have the filters built into the chip! Happy holidays to all, john On Mon, 18 Dec 2006, Alberto di Bene wrote: > John Harrison, NI1B wrote: > > Hi All, > > > > The one REAL change in recent (PCI) sound cards seems to be that the > > input low pass filter AKA anti-aliasing filter HAS BEEN ELIMINATED on > > many (all?) of the cheaper PCI sound cards. > > This probably was done because the cheap AC'97 compliant chipsets found on > the mainboards, or in the less expensive > PCI sound cards do sample at a _fixed_ rate of 48 kHz, so the anti-aliasing > filter is now fixed, no need to adjust it > when changing sampling speed. The other sampling speeds are produced by > Windows itself, as said by Leif, by a software > downsampling routine, and the anti-aliasing filtering is also done in > software, before the downsampling. > This under Windows. Under Linux, I don't know... > > 73 Alberto I2PHD > > > > ############################################################# > This message is sent to you because you are subscribed to > the mailing list <linrad@antennspecialisten.se>. > To unsubscribe, E-mail to: <[EMAIL PROTECTED]> > To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> > To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]> > Send administrative queries to <[EMAIL PROTECTED]> > ############################################################# This message is sent to you because you are subscribed to the mailing list <linrad@antennspecialisten.se>. To unsubscribe, E-mail to: <[EMAIL PROTECTED]> To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]> Send administrative queries to <[EMAIL PROTECTED]>
