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From: mykes@sega0.SF-Bay.ORG (Mike Schwartz)
Newsgroups: comp.sys.amiga.audio
Subject: Re:  Disable low-pass filter on Amiga 500?
Message-ID: <mykes.0104@sega0.SF-Bay.ORG>
Date: 24 Mar 91 06:40:02 GMT
Article-I.D.: sega0.mykes.0104
References: <1391@ssp18.idca.tds.philips.nl> <9103192231.39@rmkhome.UUCP>
Organization: Amiga makes it possible
Lines: 51

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. *
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