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Laptop Sound Improve (Effective Static Noise Reduction), How to get free of static noise of your laptopīs integrate soundcard
Misha.Cze
post May 7 2009, 21:47
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Hey guys,

I tried to search for similar thread as this one I am going to create, and did not found any posts regarding this solution. It concerns any laptop with integrated audio device and is for everyone who wants to get rid of the static noise of laptops. I will begin with my "story" - I connected my q-jays in-ear headphones to my laptop (Compal FL90v2 with Intel HD audio codec).. there was really a lot of noise disregarding the volume.. no matter what the volume is, there is still the same static noise, I guess because of the electromagnetic "storm" that the integrated audio sound card is not shielded from. Still, the codec sounds quite okay to me - has the power to quite punch the q-jays through and also the sound characterstics are a lot better compared to the ac-97 standard. Except for the noise. The idea is that the maximum possible volume to listen to is something around 20 or 25 %, and if the volume was pumped higher, the real ratio of sound/static noise can be improved greatly. But when the volume is set this high (like 70 %), the headphones are too loud to listen to. So the signalīs volume has to be reduced somehow. For this, a volume element on cable can be used. Like the Shure volume control or Koss VC20. The trick is to set high volume on laptop, and then reduce it via the cable volume control. The result is noise-free sound. There might be questions considering loss in the sound sharpness, highs, or the fullness or definition of bass, but my opinion is that this solution had much more gain the the loss, if the loss is audible anyhow. Consider this as an idea to improve any static noise problem and also feel free to experiment (or to build your own "volume control").. Here are some images for illustration; please feel free to discuss wink.gif

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pdq
post May 7 2009, 21:55
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Another possibility, if the noise is high frequency (i.e. hiss) is to use the equalizer in the laaptop to boost high frequencies, then place a passive low-pass filter, made from a resistor and a capacitor, between the laptop's output and the headphones. Playing around a little with the equalizer should allow you to get a relatively flat frequency response with greatly reduced noise.
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Misha.Cze
post May 7 2009, 22:00
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QUOTE (pdq @ May 7 2009, 19:55) *
Another possibility, if the noise is high frequency (i.e. hiss) is to use the equalizer in the laaptop to boost high frequencies, then place a passive low-pass filter, made from a resistor and a capacitor, between the laptop's output and the headphones. Playing around a little with the equalizer should allow you to get a relatively flat frequency response with greatly reduced noise.


Yeah, thanks for reply, seems like a good alternative (although maybe the volume control is more flexible when not only using with a laptop) - by the way isnīt this solution similar to the Dolby B Noise Reduction Method ? Just asking..
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DVDdoug
post May 8 2009, 00:03
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QUOTE (Misha.Cze)
...There might be questions considering loss in the sound sharpness, highs, or the fullness or definition of bass, but my opinion is that this solution had much more gain the the loss, if the loss is audible anyhow.
I wouldn't worry about that... The volume control should only affect volume. If anything, it might improve bass slightly by providing a lower load impedance (at lowered volumes)*.

QUOTE (Misha.Cze @ May 7 2009, 14:00) *
QUOTE (pdq @ May 7 2009, 19:55) *
Another possibility, if the noise is high frequency (i.e. hiss) is to use the equalizer in the laaptop to boost high frequencies, then place a passive low-pass filter, made from a resistor and a capacitor, between the laptop's output and the headphones. Playing around a little with the equalizer should allow you to get a relatively flat frequency response with greatly reduced noise.


Yeah, thanks for reply, seems like a good alternative (although maybe the volume control is more flexible when not only using with a laptop) - by the way isnīt this solution similar to the Dolby B Noise Reduction Method ? Just asking..
Dolby B is "dynamic". That is, the filtering varies depending on the high-frequency content. It's a specialized compression during encoding, with complementary expansion during decoding. But, the suggested technique is similar to RIAA LP equalization, NAB tape equalization, and if I recall correctly, FM broadcast is also equalized with a high frequency boost before transmission, and a high frequency cut after reception.



* There is usually a "DC blocking" capacitor on the output. The capacitor and load resistance/impedance together form a high-pass filter. Ideally, the filter cutoff frequency will be subsonic (with a large-enough capacitor) and this won't be an issue. (In this configuration, higher load impedance lowers the cutoff frequency, and/or higher capacitance also lowers the cutoff frequency.)

And, I'm making an assumption that the volume control potentiometer has a higher resistance than the headphones. At low volumes the potentiometer is effectlively the only load on the output. At high volume (or maximimum) settings the potentiometer will be effectively in parallel with the headphone, lowering the net impedance and increasing the cutoff frequency and possibly weakening bass (slightly).


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Axon
post May 8 2009, 02:18
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A lot of this noise can be related to current draws imposed by the CPU, which are strongly periodic due to the OS scheduler (typically with a 1ms or 10ms period). Running a program that consumes 100% CPU time, while not exactly a great use of battery life, can significantly improve SNR in some cases.
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TREX6662k6
post May 15 2009, 18:36
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Axon, I encounter the problem you describe but I believe its due to the processor dynamically clocking down or up with usage.

In Vista Power Management, if you force load and idle percentages to 100% the noise may be reduced or disappear completely. Or in XP, set the power profile to Always On.


--------------------
http://www.last.fm/user/TREX6662k5/
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saratoga
post May 15 2009, 19:52
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QUOTE (Axon @ May 7 2009, 21:18) *
A lot of this noise can be related to current draws imposed by the CPU, which are strongly periodic due to the OS scheduler (typically with a 1ms or 10ms period).


I don't think the scheduler has any real impact on current draw unless the CPU dynamically clocks itself on intervals timed with the scheduler. Thread changes themselves shouldn't have a real impact on current draw.
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