terjepe@stud.cs.uit.no (Terje Pedersen) (03/21/91)
Some time ago i found a picture that showed how to disable the filter on a A1000. But since i don't own a A1000 i didn't keep it. But now a friend of mine is in desperate need of it. The sad part is that I don't know where i found it.. Does anyone know where it is ? TP
doctorj@en.ecn.purdue.edu (Jeffrey W Davis) (03/22/91)
In article <1991Mar21.115210.7692@mack.uit.no> terjepe@stud.cs.uit.no (Terje Pedersen) writes: >Some time ago i found a picture that showed how to disable the filter on >a A1000. Someone should have told me about this sooner... my machine has been running on the SAME filter for 5 1/2 years. Is this bad for the engine(CPU)? If you are referring to the audio filter, the A1000 does not have such a nuisance. Otherwise, I am quite curious to know what filter to which you refer...? *********************************************************** * Jeff Davis * Relax! And get into /// * * doctorj@en.ecn.purdue.edu * the STRESS!!! /// * * * \\\///030 * * * -Gigahertz!- Amiga\XX/ 882 * *********************************************************** -=[ In Stereo Where Available ]=-
terjepe@stud.cs.uit.no (Terje Pedersen) (03/23/91)
It it the audio-filter I am talking about. If I am not totally mistaken the low-pass filter on a A1000 is permanently on and it can't be turned off as is possible on all the other Amigas unless you do some hardware fixing. In other words you are stuck with a poor sound output. I saw a picture that told how to do just that, and I am looking for it again. #include "some_joke_about_the_ancient_A1000.h"...
h112706@cc.tut.fi (Herranen Henrik) (03/23/91)
In article <1991Mar22.054754.9284@en.ecn.purdue.edu> doctorj@en.ecn.purdue.edu (Jeffrey W Davis) writes:
If you are referring to the audio filter, the A1000 does not have such a
nuisance. Otherwise, I am quite curious to know what filter to which you
refer...?
The A1000 does have an audio filter, and a very powerful one, too.
Period.
--
Henrik 'Leopold' Herranen Internet: h112706@cc.tut.fi
Snail Mail: TTKK/Paarakennuksen neuvonta/PL527/33101 Tampere/Finland
"I don't need no arms around me, I don't need no drugs to calm me" - PF 1979Dickson@system-m.phx.bull.com (Paul Dickson) (03/23/91)
> It it the audio-filter I am talking about. If I am not totally > mistaken the low-pass filter on a A1000 is permanently on and it > can't be turned off as is possible on all the other Amigas > unless you do some hardware fixing. In other words you are > stuck with a poor sound output. There is no audio filter on the A1000. The filter was added to the other Amigas to reduce aliasing noise on the audio output, but can be turned off by software. -Paul Dickson
johnhlee@CS.Cornell.EDU (John H. Lee) (03/25/91)
In article <48599@nigel.ee.udel.edu> Paul Dickson <Dickson@system-m.phx.bull.com> writes: >There is no audio filter on the A1000. The filter was added to the >other Amigas to reduce aliasing noise on the audio output, but can be >turned off by software. Sorry, but the A1000 does indeed have the anti-aliasing audio filters built-in. They are permanent. Later Amigas added the ability to bypass them via software. Hardware hacks have been published to add this (nice) capability to A1000's. ------------------------------------------------------------------------------- The DiskDoctor threatens the crew! Next time on AmigaDos: The Next Generation. John Lee Internet: johnhlee@cs.cornell.edu The above opinions of those of the user, and not of this machine.
ammrk@swpyr2.sbc.com (Mike R. Kraml) (03/25/91)
In article <48599@nigel.ee.udel.edu> Dickson@system-m.phx.bull.com (Paul Dickson) writes: >> It it the audio-filter I am talking about. If I am not totally >> mistaken the low-pass filter on a A1000 is permanently on and it >> can't be turned off as is possible on all the other Amigas >> unless you do some hardware fixing. In other words you are >> stuck with a poor sound output. > >There is no audio filter on the A1000. The filter was added to the >other Amigas to reduce aliasing noise on the audio output, but can be >turned off by software. > > -Paul Dickson Try again!!! Yes, the A1000 does have an "always enabled" 7kc audio filter. Its plainly in the service manual, and I have personally disabled a few myself. There was a hack put out by AC computing a few years back that allowed you to attach it to the LED similar to the way the 500/2000/3000 work, if someone is interested I'll look through my old Amazing mags. Later, Mike... -- ============================================================================= Mike Kraml - Manager-Separations Mechanization - SWBT - Finance Department One Bell Center - 30-D-06 - St. Louis, Mo. 63101 PHONE: 314-235-8012 UUCP: {uunet, bellcore, texbell}...!swpyr2.sbc.com!ammrk
peterk@cbmger.UUCP (Peter Kittel GERMANY) (03/25/91)
In article <48599@nigel.ee.udel.edu> Dickson@system-m.phx.bull.com (Paul Dickson) writes: >> It it the audio-filter I am talking about. If I am not totally >> mistaken the low-pass filter on a A1000 is permanently on and it >> can't be turned off as is possible on all the other Amigas >> unless you do some hardware fixing. In other words you are >> stuck with a poor sound output. > >There is no audio filter on the A1000. The filter was added to the >other Amigas to reduce aliasing noise on the audio output, but can be >turned off by software. Sorry, but I fear you're wrong. In the A1000 schematics I have (the old ones on one single sheet), there are definitely filters on both outputs. They are built with 5-fold RC combinations plus an LF 347 OpAmp. -- Best regards, Dr. Peter Kittel // E-Mail to \\ Only my personal opinions... Commodore Frankfurt, Germany \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk
ridder@elvira.enet.dec.com (Hans Ridder) (03/26/91)
In article <1991Mar22.054754.9284@en.ecn.purdue.edu> doctorj@en.ecn.purdue.edu (Jeffrey W Davis) writes: >If you are referring to the audio filter, the A1000 does not have such a >nuisance. Otherwise, I am quite curious to know what filter to which you >refer...? The A1000 does indeed have a filter on the audio output. As I remember, there was a hack published in some magazine (Amazing?) on how to bypass it with a circuit wired to the power light bit in one of the CIA's. Then the A500 and A2000 came out with just such a feature.... >* Jeff Davis * Relax! And get into /// * >* doctorj@en.ecn.purdue.edu * the STRESS!!! /// * -hans ------------------------------------------------------------------------ Hans-Gabriel Ridder Digital Equipment Corporation ridder@elvira.enet.dec.com Customer Support Center ...decwrl!elvira.enet!ridder Colorado Springs, CO
m0154@tnc.UUCP (GUY GARNETT) (03/27/91)
In article <48599@nigel.ee.udel.edu> Dickson@system-m.phx.bull.com (Paul Dickson) writes: >> It it the audio-filter I am talking about. If I am not totally >> mistaken the low-pass filter on a A1000 is permanently on and it >> can't be turned off as is possible on all the other Amigas >> unless you do some hardware fixing. In other words you are >> stuck with a poor sound output. > >There is no audio filter on the A1000. The filter was added to the >other Amigas to reduce aliasing noise on the audio output, but can be >turned off by software. > > -Paul Dickson For the last time, Let's Get This Straight! There is a Low-Pass audio filter installed on the audio output of all Amiga models. This filter is there to improve the audio output quality of the sound generators. It removes high-frequency artifacts (which would otherwise be audible to many people) caused by aliasing in the Amiga's audio output system. The filter starts attenuating at above 7Khz, and completely blocks everything above 14Khz. These frequencies were chosen because the Amiga's audio system has a maximum sampling rate of about 14,000 samples/second. By application of the Nyquist Theorem, artifacts will appear at approximately half of this (about 7Khz), and any sound above the sampling rate is composed of nothing but artifacts (therefore the cutoff at about 14Khz). On the Amiga 1000, this filter is built into the audio output circuitry, and cannot be controlled by software. Armed with the A1000 schematic, a talented hacker can pick up the signal before it goes to the filter, and route it to an extra set of jacks. The unfiltered signal is desirable for certain applications where the filter is un-needed (like driving galvos in a laser light show) and would simply muddy the signal. Talented programmers have also made the Amiga do things that the original hardware designers didn't consider, and so the unfiltered signal is also desirable for audio applications (where the aliasing effects will be removed by external equipment, or where the artifacts are part of the desired effect). Therefore, on all subsequent Amigas, a set of bypass switches was added to the circuit. They are controlled by the power light intensity setting: when the light is dim, the filters are switched out, and when it is bright, they are switched in. This can be controlled by setting or clearing a certain bit in the custom hardware, and many Amiga audio programs provide an option to do this. A very clever hacker figured out a way to add this capability to the Amigia 1000 (by hacking a similar circuit onto the A1000 motherboard). Amazing Computing has run articles on both hacks. Back issues are available from PiM Publications, PO Box 869, Fall River, MA 02722; telephone 1-800-345-3360. You want Vol 3 No 4 (April 1988) which contains an article "Upgrade Your Amiga 1000 to A500/2000 Audio Power" by H. Bassen. I hope all of this helps clear up the confusion. Wildstar
dltaylor@cns.SanDiego.NCR.COM (Dan Taylor) (03/27/91)
In <1991Mar22.190024.2299@mack.uit.no> terjepe@stud.cs.uit.no (Terje Pedersen) writes: >It it the audio-filter I am talking about. If I am not totally mistaken the >low-pass filter on a A1000 is permanently on and it can't be turned off as is >possible on all the other Amigas unless you do some hardware fixing. You are NOT mistaken. ALL A1000's came with a low-pass filter, just as all other Amiga's do, only the A1000's couldn't be turned off. Check back issues of "Amazing Computing", I believe, for the fix. Their fix made the A1000 filters switch, like the A500, etc. It was straight-forward, but you had to know how to solder. Dan Taylor
Paul Dickson <Dickson@system-m.phx.bull.com> (03/29/91)
From the weight of the response (especially direct mail) then I'm
definately wrong (I also look it up in the A1000 schematics). Never
trust what someone said several years ago, even if they are an Amiga
Commercial Developer. His implications weren't what I thought they
were.
So...I was wrong. Stop sending me mail! :-)
-Paul