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Old 19th January 2007, 04:42 PM   #1
405man is offline 405man  Scotland
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Default A test of the audibility of an LED illuminating a CD

I would like to test the audibility of illuminating a CD with a coloured led as many people claim that this can make a noticeable difference. What I propose is to construct a counter which displays a number which can be incremented and which controls the status of the LED in pseudorandom manner ( the exact details of the device are unimportant at the moment ). The test would be run as follows.
The counter would be reset to 1, the cd played and the status of the led would be determined by the quality of the replay and noted down. The counter would then be incremented by one a new LED status would be produced and the CD or an other CD or track played and again the quality again noted. This would be repeated a considerable number of times at the end of which would be a list of numbers and corresponding list of LED status determined by listening, this would then be compared to a list of the actual led status from which it should be possible to determine the significance of the LED on the reproduced sound. Is this a reasonable protocol to determine the audibility of the LED

Stuart
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Old 19th January 2007, 07:28 PM   #2
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Hi Stuart,

I like your style!! I'm considering the LED mod myself.
Verifying subjective results is a contentious issue around here but I think you've got the right idea.
I will certainly be very interested in your results.

The truth for me is that I will probably hear a difference if I do the mod but don't trust my own mind. Past experience has taught me that the improvement I hear is often directly proportional to the effort and enthusiasm I use.

Will you be testing with different colours?

Cheers,
Martin.
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Old 19th January 2007, 10:28 PM   #3
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It is a good idea to try to test this claim, however, no matter how well thought out your protocol, the "believers" will ultimately find something wrong with the methodology, unless of course, it validates their claims, in which case no one can make any argument against your test methodology.

Now for the technical stuff... I think your idea is good, but you need to be able to find out after-the-fact whether the LED was on or not during a praticular listening interval. If you use a pseudo random sequencer to turn the LED on or off, you can reproduce the LED sequence any time and check it after-the-fact by entering the same seed value. This could be managed by a simple microcontroller program.

If you manage to hear a difference or not, questions will arise as to how much light you used, how was it distributed in the CD drawer, and was there any possibility of the current through the LED(s) causing some audible effect. If you use a high power LED, there may also be issues of how the heat generated by the LED was removed from the CD drawer.

I think to be safe, some sort of light pipe or fiber optic coupling should be used so that the LED and it's current source can be loacted well away from the CD player, or at least the CD drawer.

Will the intervals also be of random length or will they be equally long? Will the listener know when the interval has elapsed of will he/she simply be listening and recording his/her impression at regular intervals? For example, if the LED on/off intervals are random between 2 and 3 minutes, have the listener mark his/her impression every 10 seconds, and don't allow them to know the beginning or end of a LED on/off interval.

Obviously, the CD player should be located out of sight of the listener lest the LED status be visible to them.

Finally, without a human to verify that the LED is actually on or off during any given interval, you'll run afoul of the "if a tree falls in the forest and there's no one there to hear it, does it make any sound?" college philosophy drop-outs. You just can't educate some people...

I_F
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Old 19th January 2007, 11:59 PM   #4
soongsc is offline soongsc  Taiwan
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Like with any thesis, there will be people that question, this really should not stop us from finding answeres to questions we have. Hope it all goes well.
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Old 20th January 2007, 12:27 AM   #5
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its easy - according to so called audiophiles EVERYTHING makes a difference in audio.
So, the easiest - stop breathing while listening. Solves all audio problems.
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Old 20th January 2007, 12:39 AM   #6
zBuff is offline zBuff  New Zealand
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So does a LED suppose to actually do? It suppose to make the CD easier to read isn't it? Could it possible to test it by just installing a LED in a computer CDrom drive and running testing using EACs extraction?
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Old 20th January 2007, 05:35 AM   #7
poynton is offline poynton  United Kingdom
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What about using one of the older models eg Philips CD104 which had an error light.?
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Old 20th January 2007, 08:54 AM   #8
Pano is offline Pano  United States
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This is a strange idea. Wouldn't extra light on the CD make the sound worse?

What is the LED light supposed to do? Bias the photo diode or something?
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Old 20th January 2007, 10:08 AM   #9
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by panomaniac
This is a strange idea. Wouldn't extra light on the CD make the sound worse?

What is the LED light supposed to do? Bias the photo diode or something?
A valid point - hence the experiment!

It should be noted that some early players eg cd303 had green tray lights as standard.

Andy
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Old 20th January 2007, 01:07 PM   #10
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by audio-kraut
its easy - according to so called audiophiles EVERYTHING makes a difference in audio.
So, the easiest - stop breathing while listening. Solves all audio problems.
Sometimes that happens.
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