Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!unmvax!pprg.unm.edu!hc!lll-winken!uunet!cbmvax!heimat!sneakers
From: sneakers@heimat.UUCP (Dan "Sneakers" Schein)
Newsgroups: comp.sys.amiga
Subject: Re: Low Pass Filter
Message-ID: <8284.AA8284@heimat>
Date: 12 May 89 23:09:32 GMT
Followup-To: comp.sys.amiga
Organization: Sneakers Computing
Lines: 68

In Message <434@tandem.Tandem.com>, leo@tandem.Tandem.com (Leo Hejza) writes:

>Now the questions, How do I turn off the D/A low pass filter. I'm playing
>28K+ samples /second back and want to recover all the information which
>is there. I already pass the output through a steep digital low pass
>filter below the Nyquist frequency so aliasing won't be a problem.

  Heres the code I wrote for AmigaMail awhile back.....

---<CUT HERE>---
/* Toggle the 500 & B2000 sound filter on/off */
/* 10-JAN-88   Dan Schein - Commodore (CATS)  */

#include <exec/types.h>
#include <stdio.h>
#include <hardware/cia.h>
#include <hardware/custom.h>
#include <hardware/intbits.h>

extern struct CIA ciaa;

UBYTE oldbits;

void main(), SetFilter(), RestoreFilter();

void main()
{
    SetFilter();                   /* Turn filter OFF                 */

    Delay(45);                     /* Do your thing here.........     */

    RestoreFilter();               /* Restore filter to original      */
}

void SetFilter()
{
    Disable();                     /* Let me alone!                   */
    oldbits = ciaa.ciapra;         /* Get the current state of filter */
    ciaa.ciapra |= CIAF_LED;       /* Force the filter off            */
    Enable();                      /* All done :-)                    */
}

void RestoreFilter()
{
    Disable();                     /* Let me alone!                   */
    if (!(oldbits & CIAF_LED))     /* Check to see if filter was on   */
    {                              /* Filter was on - turn it back on */
        ciaa.ciapra &= (~ CIAF_LED);
    }
                                   /* Filter was off - leave it off   */
    Enable();                      /* All done :-)                    */
}
---<CUT HERE>---

   AmigaMail is published by CATS 12 times a year and is included FREE to all
   Commercial/Certified developers -or- via a subscription. Look into it,
   there great reading and they make great refrence material ;-)

   Sneakers

--
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