Power led and sound

[lilalurl]

Not a problem but I thought of this because of the threads about the motherboards "unknown" ports.


I remember that within a few games some sound effects triggered a kind of sound filter that decreased the light from the power led (1200 and 600, I don't know for 500).

In Dune (french version) there was a key toggling between the filtered and non-filtered sound.

And in Lotus II, during the second race, when driving under a tunnel this "filtering" system was used to provide an echo/enveloppe effect.

I can't find the key for Dune anymore, but I checked, the effect is emulated in Lotus II.

Anybody knowing more about the reasons of the LED change ? And what was the purpose of this filter ?

And will the LED change be one day emulated :-p?

04/XII/2009 edit: Just tested with Dune in Winuae, after someone started another thread about the LED dimming. With on-screen LEDs activated, you get visual cue of the filter activation.

The toggle key in Dune is F3, but you have to press another key (any key) between each press, otherwise it won't do anything.

[Mr Softy]

I think it was some sort of filter that boosted the high frequencies. At least in DSS3 (a tracker) it sounded this way, more hissy! There was a hex command to toggle it within a song, or you could just press a button on the GUI for a permanent effect.

I remember also wondering why the LED was fading when the filter was on.

Anyone knowing more about this?

[thomas]

The Amiga has a low-pass filter for sound. It reduces high-frequency noise. When using high-quality samples (without noise), the filter can be deactivated, which sounds slightly better.

The filter and the power LED are controlled by the same bit in memory, so the LED and the filter always are activated or deactivated together.

[Severin]

iirc, executive used the power led to show cpu usage, pity it also totally messed up any sound by switching the filter many times a second

There are a few programs on aminet to set the filter (I use multicx)...

http://wuarchive.wustl.edu/pub/amine.../SetFilter.lha

http://wuarchive.wustl.edu/pub/amine...hack/flipf.lha

http://wuarchive.wustl.edu/pub/amine...illfilters.lha

http://wuarchive.wustl.edu/pub/aminet/util/misc/LED.lha

[gary]

The Amiga has a low-pass filter for sound. It reduces high-frequency noise. When using high-quality samples (without noise), the filter can be deactivated, which sounds slightly better.

True. The filter may have been useful for low quality samples that were expected to be used with the original Amiga (256k RAM) but the vast majority of samples (especially in MODs) sounded much better with the filter turned off. Unfortunately the default value of the lowpass filter was ON when the Amiga powered up which means that if a programmer forgot to switch it off the game music would sound muffled.
Music disks used the filter to simulate the "Dolby" button on stereos

[Chuckles]

On the 500 (at least on the older ones such as mine), when the low-pass filter was turned off, the power light didn't just dim. It went out completely. I still remember how much it freaked me out when I just happened to notice it the first time I was booting into a game that turned the filter off. I had never heard of this feature before, and I feared that I was developing some sort of hardware problem. It certainly wasn't a feature of the hardware that Commodore expended any effort to point out to buyers, but it sometimes really had a positive effect on the quality of music.

[Phiber]

Hmmh.. i wonder if this also applies into my CD32...

I started to wonder, why the led's dim down after i start loading something from the CD...

[spiff]

The filter was kinda annoying..
I’ve always wondered why the sound interpolation routines sound about the same? (as in uae) Just like filter that just cuts the high frequencys.
I thought sound interpolation would increase the sound quality.. or at least not degrade it…