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5.4 Noisy audio measurements
I have been solving almost whole the time when using 6800le-card quite annoying audio/noise problems. This problem has been very hard to solve, and took long time to solve it or find a sensible reason. Now I am sure that problem is caused ONLY due to GW6800le-card, and therefore I will explain the 'feature' in this document. It is likely, that the same problem disturbs also other users having a BS-card and I have demostrated excatly the same behaviour with a card never (yet) shown BS-feature.
The problem is simply a annoying sound or noise, having varing frequency and amplitude. Moreover, the frequency is 'modulated' with the current framerate (!!). Usually the noise has quite low amplitude and it can be only heard when there are no other sounds. For instance a 3dmark03-benchmark is good for testing purposes, since it does not have (mostly part) sound and the framerate is varing considerably. Following setup is required for the audio test:
- Computer having a GF6800(le)-card, that is known/assumed to be BS-affected
- CD-rom having audio cable installed to soundcard/mainbourd (important!!)
- In the 'Volume control'-panel the 'CD-player Volume' is maximized
- A suitable program is launched e.g. 3dmark03 or aquamark03 (without sound)
- Headphones preferred, since the amplitude of the noise might be low
- Just listen ..
Why I am sure it is caused by GF6800 ? I have tested a lot following different options/combinations:
- GF4200 : No noise
- GW6800le version 2 vs version 1b : No difference !!! version 1b has not made BS (yet) !!!
- Win98 vs Win2000 : No difference
- Sounblaster Audigy vs integrated : No difference
- Different CD-players : Minor difference (DVD-player makes louder noise, since it consumes more current)
- Molex removed from CD : No noise
- Added 'filter' to CD-molex : Very low noise
The filter I used is constructed with wires ripped from old PC-power and a large ferrite ring (ferrite rings can also be 'found' from old electronic equipments e.g. power supplies). The molex-wires have been cut in the middle and wounded several times around the ferrite. Finally wires are soldered together again, see figure below.
Figure 14. A highpass filter for removing power supply noise due to GF6800-card
In order to have some idea what kind of sound you would except, I recorded following audio tracks (amplified a lot): 'Windows 2000 - do nothing', ' 3dmark03 GT1', 'Aquamark03' and 'SkiAlpin'. If interested, download and enjoy
http://www.angelfire.com/electronic...in2000_idle.mp3
http://www.angelfire.com/electronic..._3dmark03_1.mp3
http://www.angelfire.com/electronic...io_aqua03_1.mp3
http://www.angelfire.com/electronic...skiapline_1.mp3
Why this is happening ??? And why it is happening also for card never made a BS-feature ? Does this noise predict BS-feature in future (if not yet affected) ?!?! I have a theory and I will explain it in more detail in the next release. In short (for this release) I think that switching regulator for memories is OSCILLATING at quite low frequency and this adds noise to the molex lines (mainly 5V).The noise is coupled via CD-player to the audio cable, due to poor power supply rejection ratio at low frequencies.
Afterwords:
I hope someone likes this document, at least for me solving this problem has been quite challenging and even sometimes fun ! I hope that you can help to make this document even better by posting answers releted to 'Most wanted' items.