[ltp] noise in audio on T430s

[Dmitry Mikhailov]

On 09/26/2013 07:35 PM, Richard Neill wrote:
>
>>
>>> Lastly, what kind of noise do you get? Is it hum, hiss, or 
>>> interference?
>>> The noise-cancelling headphones can also add a very high-pitched, 
>>> quiet,
>>> squeak (sounds like an analog TV flyback coil) sometimes.
>>
>> I get a quiet susurration, very similar to white noise.  It stops when I
>> unplug the headphones from the T430s, so I guess that's the source.
>> Also, when I scroll a PDF, I get a faint, irregular scratch-like noise.
>
> That's what I hear. The white noise is just the various amplifiers 
> being less than perfect.
When nothing is being played, sound system should shut itself down so 
you won't hear anything. It clicks when shuts down and clicks again when 
activates. At least on x41, x60, x61, t61.

It can be activated by:
# cat /etc/modprobe.d/custom.conf |grep snd
options snd_hda_intel power_save=2

Read more:
# modinfo snd_hda_intel|grep power_save\:
parm:           power_save:Automatic power-saving timeout (in second, 0 
= disable). (xint)


> The "scratching" is the CPU going in and out of sleep, and the 
> corresponding changes in load in the switch mode PSU, which 
> inductively couples into the audio circuit.

You can get rid of it by totally disabling the CPU power saving - 
obviously not recommended for mobile use:
#echo performance > /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor

It can be reversed to normal power saving 'ondemand' mode:
#echo ondemand > /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor

I bet you can script that via power management scripts (like pm-utils 
maybe).

-- 
Best regards,
         Dmitry Mikhailov