Power LED dimming - why?

Muzer · 03 December 2009, 19:19

Some games, I've noticed, dim the power LED when they start - and if not, occasionally the WHDLoad slave will do it. I seem to remember reading somewhere that this improves the sound quality - can anyone expand on why this is and what exactly it does? I did do a few searches but they returned nothing relevant, so if there has already been a thread I apologise.

Coagulus · 03 December 2009, 19:25

copied from wiki

The Amiga contains an analog low-pass filter (reconstruction filter) which is external to Paula. The filter is a 12 dB/oct Butterworth low-pass filter at approximately 3.3 kHz. The filter can only be applied globally to all 4 channels. In models after the Amiga 1000, the brightness of the power LED is used to indicate the status of the filter. The filter is active when the LED is at normal brightness, and deactivated when dimmed (on early Amiga 500 models the LED went completely off). Models released before Amiga 1200 also have a static "tone knob" type lowpass filter that is enabled regardless of the optional "LED filter". This filter is a 6 dB/oct lowpass filter with cutoff frequency at 4.5 or 5 kHz.

lilalurl · 04 December 2009, 02:26

A past discussion here:
http://eab.abime.net/showthread.php?t=9313

PowerPie5000 · 04 December 2009, 03:13

I have a couple of the older A500's and the power led turns off completely when the audio filter is disabled! One a500 uses a rev 3 motherboard (red power led) and the other is a rev 5 (green power led).

I'm not too sure which A500 revision introduced dimming of the power led?

Jope · 04 December 2009, 08:41

Rev6

PowerPie5000 · 04 December 2009, 14:27

Quote:

Originally Posted by Jope

Rev6

Thanks for clearing that up

alexh · 04 December 2009, 15:08

I used to love demo's which did strange things with this feature. PWM the filter on and off to create strobe effects.

rkauer · 05 December 2009, 07:37

Alexh, can you name those demos? I'm interested in see this "feature" in action.

03 December 2009, 19:19	#1
Muzer Registered User Join Date: Sep 2009 Location: UK Posts: 146	Power LED dimming - why? Some games, I've noticed, dim the power LED when they start - and if not, occasionally the WHDLoad slave will do it. I seem to remember reading somewhere that this improves the sound quality - can anyone expand on why this is and what exactly it does? I did do a few searches but they returned nothing relevant, so if there has already been a thread I apologise.

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03 December 2009, 19:25	#2
Coagulus Gets there in the end... Join Date: Sep 2005 Location: Wales Posts: 862	copied from wiki The Amiga contains an analog low-pass filter (reconstruction filter) which is external to Paula. The filter is a 12 dB/oct Butterworth low-pass filter at approximately 3.3 kHz. The filter can only be applied globally to all 4 channels. In models after the Amiga 1000, the brightness of the power LED is used to indicate the status of the filter. The filter is active when the LED is at normal brightness, and deactivated when dimmed (on early Amiga 500 models the LED went completely off). Models released before Amiga 1200 also have a static "tone knob" type lowpass filter that is enabled regardless of the optional "LED filter". This filter is a 6 dB/oct lowpass filter with cutoff frequency at 4.5 or 5 kHz.

04 December 2009, 02:26	#3
lilalurl Global Moderator Join Date: Aug 2001 Location: France Posts: 3,289	A past discussion here: http://eab.abime.net/showthread.php?t=9313

04 December 2009, 03:13	#4
PowerPie5000 Miggy Ate My Hamster! Join Date: Nov 2008 Location: Lancashire, UK Posts: 1,566	I have a couple of the older A500's and the power led turns off completely when the audio filter is disabled! One a500 uses a rev 3 motherboard (red power led) and the other is a rev 5 (green power led). I'm not too sure which A500 revision introduced dimming of the power led?

04 December 2009, 08:41	#5
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	Rev6

04 December 2009, 15:08	#7
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,337	I used to love demo's which did strange things with this feature. PWM the filter on and off to create strobe effects.

05 December 2009, 07:37	#8
rkauer I hate potatos and shirts Join Date: Oct 2007 Location: Sao Leopoldo / Brazil Age: 58 Posts: 3,482	Alexh, can you name those demos? I'm interested in see this "feature" in action.

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