fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) (03/13/91)
How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) Audimaster II has this option, but when I use it I can not hear any sound improvement, although the red power light turns off. The soundsamples I use are made with samplingrates higher then 30khz, and the Amiga is connected to my hifi-equipment. But I can not hear any differences in soundoutput using audiofilter enabled or disabled, the soundoutput still has no high-frequencies. Do I need to open my Amiga for soldering? Thank you very much for any help. Ferdinand van Ommen. -- -- Ferdinand van Ommen -- fwvo@idca.tds.philips.nl -- ..!mcvax!philapd!fwvo --
s117986@lehtori.tut.fi (Salmij{rvi Janne) (03/14/91)
From article <1391@ssp18.idca.tds.philips.nl>, by fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen): > > How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) > Audimaster II has this option, but when I use it I can not hear any > sound improvement, although the red power light turns off. > The soundsamples I use are made with samplingrates higher then 30khz, and > the Amiga is connected to my hifi-equipment. But I can not hear any > differences in soundoutput using audiofilter enabled or disabled, > the soundoutput still has no high-frequencies. > > Do I need to open my Amiga for soldering? > > Thank you very much for any help. > > Ferdinand van Ommen. > -- > -- Ferdinand van Ommen -- fwvo@idca.tds.philips.nl -- ..!mcvax!philapd!fwvo -- I think you have an ancient A500 on which the filter just doesn't exist. Otherwise just set 2nd bit on $bfe001. -- Janne Salmij{rvi s117986@cc.tut.fi
dvljhg@cs.umu.se (J|rgen Holmberg) (03/16/91)
In article <1991Mar14.104334.15725@cc.tut.fi> s117986@lehtori.tut.fi (Salmij{rvi Janne) writes: > >From article <1391@ssp18.idca.tds.philips.nl>, by fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen): >> >> How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) >> Audimaster II has this option, but when I use it I can not hear any >> sound improvement, although the red power light turns off. >> The soundsamples I use are made with samplingrates higher then 30khz, and >> the Amiga is connected to my hifi-equipment. But I can not hear any >> differences in soundoutput using audiofilter enabled or disabled, >> the soundoutput still has no high-frequencies. >> >> Do I need to open my Amiga for soldering? >> >> Thank you very much for any help. >> >> Ferdinand van Ommen. >> -- >> -- Ferdinand van Ommen -- fwvo@idca.tds.philips.nl -- ..!mcvax!philapd!fwvo -- > >I think you have an ancient A500 on which the filter just doesn't exist. >Otherwise just set 2nd bit on $bfe001. > Aaarrgghh! There are no A500 without lowpass filters, no matter how ancient! From your description it seems that you have an old machine where it was not possible to turn off the lowpass filter in software. You will need to bypass the filter in hardware. I don't have the circuitry around so I can't tell you exactly how to do that but the circuit display in the manual shows the filter in detail. When you do solder, make that a switchable bypass. That way you can avoid some nasty overtones if you want to :-) /Jorgen -- email dvljhg@cs.umu.se | DUMII: Sentinel of the scales Everything I say is always true, just apply it to the right reality. "Credo, quia absurdum est." Credo (dei) in absurdum est?
rmk@rmkhome.UUCP (Rick Kelly) (03/20/91)
In article <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: >How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) >Audimaster II has this option, but when I use it I can not hear any >sound improvement, although the red power light turns off. >The soundsamples I use are made with samplingrates higher then 30khz, and >the Amiga is connected to my hifi-equipment. But I can not hear any >differences in soundoutput using audiofilter enabled or disabled, >the soundoutput still has no high-frequencies. >Do I need to open my Amiga for soldering? The average human being cannot hear anything above 15khz. Good stereo equipment cannot produce sound above about 18khz. It is a simple fact of life. There is no reason for you to open up your 500. Rick Kelly rmk@rmkhome.UUCP frog!rmkhome!rmk rmk@frog.UUCP
andand@cia.docs.uu.se (Anders Andersson) (03/20/91)
In <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: >How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) >Audimaster II has this option, but when I use it I can not hear any >sound improvement, although the red power light turns off. >The soundsamples I use are made with samplingrates higher then 30khz, and >the Amiga is connected to my hifi-equipment. But I can not hear any >differences in soundoutput using audiofilter enabled or disabled, >the soundoutput still has no high-frequencies. >Do I need to open my Amiga for soldering? If your Amiga is a very early model then: yes, soldering is required, else it can be done by turning of the power light in software, quick and dirty (the way you shouldn't do it - but everybody does it) by setting or clearing a bit at 12574721 decimal (I think). -Anders Andersson (andand@cia.docs.uu.se - mail just *might* get through, but I wouldn't bet on it)
ags@scs.carleton.ca (Alexander George Morison Smith) (03/22/91)
In article <9103192231.39@rmkhome.UUCP> rmk@rmkhome.UUCP (Rick Kelly) writes: >In article <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: >>How can I disable the low-pass filter on my Amiga 500? ... > >The average human being cannot hear anything above 15khz. Good stereo >equipment cannot produce sound above about 18khz. It is a simple fact of >life. There is no reason for you to open up your 500. The Amiga audio filter cuts off at 7KHz, I believe. So it is still worthwhile to disable it. Besides that, the sampling rate has to be twice the frequency if you want to reproduce sounds of a given frequency. Even higher sampling rates improve the quality of the sound. As you may know, compact disks are recorded at a rate of 14KHz. - Alex
dvljhg@cs.umu.se (J|rgen Holmberg) (03/22/91)
In article <9103192231.39@rmkhome.UUCP> rmk@rmkhome.UUCP (Rick Kelly) writes: >In article <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: > >>How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) >>Audimaster II has this option, but when I use it I can not hear any >>sound improvement, although the red power light turns off. >>The soundsamples I use are made with samplingrates higher then 30khz, and >>the Amiga is connected to my hifi-equipment. But I can not hear any >>differences in soundoutput using audiofilter enabled or disabled, >>the soundoutput still has no high-frequencies. > >>Do I need to open my Amiga for soldering? > > >The average human being cannot hear anything above 15khz. Good stereo >equipment cannot produce sound above about 18khz. It is a simple fact of >life. There is no reason for you to open up your 500. > > The lowpass filter cuts off sound at 7Mhz, if you disable it you will get sound up to about 14 Mhz. The difference is great! ( Even I hear it ;-) ) /Jorgen -- email dvljhg@cs.umu.se | DUMII: Sentinel of the scales Everything I say is always true, just apply it to the right reality. "Credo, quia absurdum est." Credo (dei) in absurdum est?
ags@scs.carleton.ca (Alexander George Morison Smith) (03/22/91)
In article <1991Mar21.201950.14705@ccs.carleton.ca> ags@scs.carleton.ca (Alexander George Morison Smith) writes: >As you may know, compact disks are recorded at a rate of 14KHz. Slight typo there, should be 44KHz not 14. - Alex
drysdale@cbmvax.commodore.com (Scott Drysdale) (03/23/91)
In article <1991Mar22.015657.20512@cs.umu.se> dvljhg@cs.umu.se (J|rgen Holmberg) writes: [ misc stuff about audio filters deleted ] >The lowpass filter cuts off sound at 7Mhz, if you disable it you will get >sound up to about 14 Mhz. The difference is great! ( Even I hear it ;-) ) i wish i could hear 14mhz. then i wouldn't need an oscilloscope to debug those home projects. >/Jorgen --Scotty -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Scott Drysdale Software Engineer Commodore Amiga Inc. UUCP {allegra|burdvax|rutgers|ihnp4}!cbmvax!drysdale PHONE - yes. "Have you hugged your hog today?" =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
kent@swrinde.nde.swri.edu (Kent D. Polk) (03/24/91)
In article <20058@cbmvax.commodore.com> drysdale@cbmvax.commodore.com (Scott Drysdale) writes: >In article <1991Mar22.015657.20512@cs.umu.se> dvljhg@cs.umu.se (J|rgen Holmberg) writes: > >[ misc stuff about audio filters deleted ] > >>The lowpass filter cuts off sound at 7Mhz, if you disable it you will get >>sound up to about 14 Mhz. The difference is great! ( Even I hear it ;-) ) > >i wish i could hear 14mhz. then i wouldn't need an oscilloscope to debug >those home projects. Just pull out your handy 50 MHz Amiga digitizer and then downconvert it using that nice built-in 4-channel synthesizer :^) Actually, the auditory system handles information a bit different than the visual & you would have to re-present the waveform information in a manner which allows the aural system to identify what you want identified (the easy one). Patter-recognition techniques can be used also. Recent research on the subject appears to show that the same Gestalt rules developed for visual perception apply in the aural realm, but are implemented a bit differently. The auditory system is 'stream' oriented, i.e. lower brain activities attempt to group acoustic 'events' in preparation for higher brain identification activities. Unfortunately, we can only attend to one stream at a time. (I have been doing some research along this line using Amigas) Kent Polk: Southwest Research Institute (512) 522-2882 Internet : kent@swrinde.nde.swri.edu UUCP : $ {cs.utexas.edu, gatech!petro, sun!texsun}!swrinde!kent
mykes@sega0.SF-Bay.ORG (Mike Schwartz) (03/24/91)
In article <9103192231.39@rmkhome.UUCP> rmk@rmkhome.UUCP (Rick Kelly) writes: >In article <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: > >>How can I disable the low-pass filter on my Amiga 500? (workbench 1.2) >>Audimaster II has this option, but when I use it I can not hear any >>sound improvement, although the red power light turns off. >>The soundsamples I use are made with samplingrates higher then 30khz, and >>the Amiga is connected to my hifi-equipment. But I can not hear any >>differences in soundoutput using audiofilter enabled or disabled, >>the soundoutput still has no high-frequencies. > >>Do I need to open my Amiga for soldering? > > >The average human being cannot hear anything above 15khz. Good stereo >equipment cannot produce sound above about 18khz. It is a simple fact of >life. There is no reason for you to open up your 500. > > > >Rick Kelly rmk@rmkhome.UUCP frog!rmkhome!rmk rmk@frog.UUCP Turning off the low-pass filter does make a difference in the audio quality of the Amiga. It is trivial to do in software. All you have to do is to turn off the Power LED and the filter is turned off too. The LED is controlled by bit #1 of CIAB PORT A ($bfe001). Try the following programs using your favorite assembler: * Program1: * Turn off LED & Filter BSET #1,$BFE001 RTS END * Program2: * Turn on LED & Filter BCLR #1,$BFE001 RTS END These programs assemble to a 48 byte executable, each, which is why | | | | | v v v v v -- ******************************************************* * Assembler Language separates the men from the boys. * *******************************************************
mykes@sega0.SF-Bay.ORG (Mike Schwartz) (03/24/91)
In article <1991Mar21.201950.14705@ccs.carleton.ca> ags@scs.carleton.ca (Alexander George Morison Smith) writes: >In article <9103192231.39@rmkhome.UUCP> rmk@rmkhome.UUCP (Rick Kelly) writes: >>In article <1391@ssp18.idca.tds.philips.nl> fwvo@idca.tds.PHILIPS.nl (Ferdinand van Ommen) writes: >>>How can I disable the low-pass filter on my Amiga 500? ... >> >>The average human being cannot hear anything above 15khz. Good stereo >>equipment cannot produce sound above about 18khz. It is a simple fact of >>life. There is no reason for you to open up your 500. > >The Amiga audio filter cuts off at 7KHz, I believe. So it is still >worthwhile to disable it. Besides that, the sampling rate has to be >twice the frequency if you want to reproduce sounds of a given >frequency. Even higher sampling rates improve the quality of the sound. >As you may know, compact disks are recorded at a rate of 14KHz. > >- Alex Compact disks are recorded at a rate of 44.1KHz using 16-bit samples for 2 channels (left/right). You are right that higher sampling rates improve the quality of the sound. They also take up lots more memory. I already posted that you can easily turn off and on the filter with software using one instruction in assembler language. Lookup bit #1 of CIA A PORT A in your hardware manual. mykes -- ******************************************************* * Assembler Language separates the men from the boys. * *******************************************************
dvljhg@cs.umu.se (J|rgen Holmberg) (03/24/91)
In article <20058@cbmvax.commodore.com> drysdale@cbmvax.commodore.com (Scott Drysdale) writes: >In article <1991Mar22.015657.20512@cs.umu.se> dvljhg@cs.umu.se (J|rgen Holmberg) writes: > >[ misc stuff about audio filters deleted ] > >>The lowpass filter cuts off sound at 7Mhz, if you disable it you will get >>sound up to about 14 Mhz. The difference is great! ( Even I hear it ;-) ) > >i wish i could hear 14mhz. then i wouldn't need an oscilloscope to debug >those home projects. > >>/Jorgen > > --Scotty Ok, ok, you have made your point guys! Late at night, no sleep, no brain - no pain etc. This should of course be 7khz and 14khz ( appr.). Just for the record, I do navigate via ultrasonic radar ;-) /Jorgen -- email dvljhg@cs.umu.se | DUMII: Sentinel of the scales Everything I say is always true, just apply it to the right reality. "Credo, quia absurdum est." Credo (dei) in absurdum est?
clemon@lemsys.UUCP (Craig Lemon) (03/25/91)
In a message posted on Thu, 21 Mar 1991 20:19:50 GMT,
ags@scs.carleton.ca (Alexander George Morison Smith) wrote:
AGMS>The Amiga audio filter cuts off at 7KHz, I believe. So it is still
AGMS>worthwhile to disable it. Besides that, the sampling rate has to be
AGMS>twice the frequency if you want to reproduce sounds of a given
AGMS>frequency. Even higher sampling rates improve the quality of the sound.
AGMS>As you may know, compact disks are recorded at a rate of 14KHz.
^^^^^
AGMS>- Alex
That's 44.1 kHz. CDs are also oversampled anywhere from 2 to 256
times depending on your DAC. There are also PWM/PDM (Pulse Width/Density)
conversion schemes as opposed to the traditional 8/12/16/18/20 bit DAC
chip. A straight 44.1kHz Amiga sample will not sound as good as a CD
because of both the oversampling and number of bits resolution. CDs have
12 bit resolution I believe (may be 16 but I don't think so). The extra
bits in vertain DAC convertors are for internal interpolation done by
oversampling.
I know this isn't totally Amiga relavent but this previous
post will probably lead to "My 14 kHz samples don't sound like CDs" and
"So if I use XXX sampler I can get CD quality audio" type posts.
--
Craig Lemon - Kitchener, Ontario. Amiga B2000/10--UUCP 1.06D/Gnews v1.1/UUCP+
clemon@lemsys.UUCP or lemsys!clemon@xenitec.on.ca | Mail any files to 'files'
xenitec!lemsys!clemon@watmath.uwaterloo.ca | at site lemsys whatever
....!{uunet}!watmath!xenitec!lemsys!clemon | path you take :-)abrown@hpcvca.CV.HP.COM (Allen Brown) (03/25/91)
>> The lowpass filter cuts off sound at 7Mhz, if you disable it you will get >> sound up to about 14 Mhz. The difference is great! ( Even I hear it ;-) ) >> Jorgen > i wish i could hear 14mhz. then i wouldn't need an oscilloscope to debug > those home projects. > --Scotty Its not always a blessing. I can hear up to 22KHz. Televisions drive me nuts. Even these 18KHz multiscan monitors bother me. And some of those "ultrasonic" burglar alarms make it impossible for me to think straight. But what really gets my goat is when some bozo tries to tell me that I cannot possibly hear these things because human hearing does not extend beyond 15KHz or 18KHz or whatever. -- Allen Brown abrown@cv.hp.com or abrown%hpcvca@hplabs.hp.com or hplabs!hpcvca!abrown or "Hey you!" Not representing my employer. A man gazing at the stars is proverbially at the mercy of the puddles in the road. ---Alexander Smith
jms@tardis.Tymnet.COM (Joe Smith) (04/10/91)
I posted this article just after the newsgroup arrived at my site.
Since the group was so new, it might not have been picked up by very
many sites, so I'm posting it again.
Article 1 of comp.sys.amiga.audio:
Path: tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.audio
Subject: Cases where the low-pass filter is a Good Thing.
Message-ID: <1418@tardis.Tymnet.COM>
Date: 13 Jan 91 07:46:13 GMT
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: BT Tymnet, San Jose, CA
Lines: 22
I was wandering around a the MacWorld Expo today, checking out the new
products. One thing that struck me was that most of the digitized
audio output did not have a low-pass filter, and it sounded awful.
Imagine an audio distorter that, whenever it detects a 2000 Hz tone,
it adds a 6000 Hz tone. And when it detects a 1000 Hz tone, it
adds a 7000 Hz tone. (When the main sound has a descending pitch,
the distortion has a rising pitch.) When human speech is passed
through such a distorter, it produces an awful high pitched rattle.
The above description is exactly what happens when an audio sample
is digitized at 8000 Hz, and played back on a system that does not
have a low-pass filter to get rid of the aliasing due to heterodyning.
My point is: Be thankful that the Amiga has a low-pass filter on the audio
outputs as standard equipment. At medium and low sampling rates, its
presence causes a noticable improvement in audio quality.
--
Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com
BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms
PO Box 49019, MS-C51 | BIX: smithjoe | CA license plate: "POPJ P," (PDP-10)
San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga 3000 speaks for me."maverjj@mentor.cc.purdue.edu (John Maver) (04/11/91)
Where is Protracker? Hmmmm? Nix