Subject: Filter emulation tips

From: shd
Date: Fri Oct 28 01:19:06 2005

To: Kohina-UADE-Forum
To test whether a song uses filter or not, grab the latest CVS release, and do:

 uade123 -v SONG

-v enables verbose mode, and filter mode changes are reported on the command line. One will see something like this if filter is used:

Playing time position 61.9s in subsong 1                
Message: Filter ON
Playing time position 61.9s in subsong 1                
Message: Filter OFF

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From: amadeus
Date: Fri Oct 28 20:38:51 2005

To: Kohina-UADE-Forum
[quote:af8f7dcf27="shd"]To test whether a song uses filter or not, grab the latest CVS release, and do:
[/quote:af8f7dcf27]

I have been wondering; Why did the Amiga have a filter mode? Did it have a purpose other than being a SFX?

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From: shd
Date: Sat Oct 29 01:53:10 2005

To: Kohina-UADE-Forum
[quote:53f7a19da3="amadeus"]
I have been wondering; Why did the Amiga have a filter mode? Did it have a purpose other than being a SFX?[/quote:53f7a19da3]

Engineers like blinking leds??

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From: amadeus
Date: Mon Oct 31 01:30:12 2005

To: Kohina-UADE-Forum
[quote:2fd1323c29="shd"]Engineers like blinking leds??[/quote:2fd1323c29]

Good answer =)

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From: alankila
Date: Sun Nov 13 20:51:35 2005

To: Kohina-UADE-Forum
I believe the idea was to make very low sample rates more usable. If I understood correctly, the Amiga 1000 had the "LED filter" permanently turned on for this reason. This was probably not a very good choice from a musical viewpoint as it seriously limited what the Amiga could do in the treble.

It seems that for A500 commodore fixed that issue by allowing optionally disabling the filter but they still left one treble-attenuating RC filter, similar to the tone knobs found on many stereo sets. This is a fairly sensible musical choice as the Amiga 500 simply can not produce frequencies freely in the upper part of the treble (say, over 8 kHz). This was because of the maximum sampling rate that limited output to something like 15 kHz, and above that frequency aliasing would occur anyway due to how Paula works. (And if sample is played at a lower frequency the aliasing will simply occur earlier.)

For A1200, they finally removed all filters from the output path, but designed the LED filter to have similar response as with A500. So, the Amiga 1200 thus was a true hi-fi machine apart from its 8-bit per sample handicap. A1200 was also able to exceed the 15 kHz maximum sampling rate limitation with different graphics modes, so I believe it made sense to get rid of the filter too.