• Registered: 2008-01-01
  • Posts: 3,025

Topic: Analysing PWM/brightness induced noise of a TFT display

I am trying to analyze (find the source) of noise/sinusoid tones that are produced by the PWM/brightness control of my TFT display. Its frequencies shift depending on the current brightness setting and I suspect that there are more than one component producing sound. My plan was to identify the components and try to keep them from swinging (like finding swinging coils and such).

Unfortunately I was not able yet to visualize the frequencies via DIGIcheck at all, they just seem to be too close to the general background noise level in my room. But I can clearly identify them via ear and after removing the backside panel of my TFT I can also make out the general areas by close-earing smile. Still bringing a microphone near these areas doesn't seem to make any difference with the spectrum analyzer.

Could anyone please give me a hint how to setup DIGIcheck and my FF400 to identify high frequency tones of low levels in order to find the source of the tones with a microphone?

Microphones I have at hand are:

Shure Beta 87a (small electret condenser) - hypercardoic
Shure Unidyne III (dynamic) - cardoic
Neuman TLM-103 (large diaphragm condenser) - cardoic
Behringer ECM 8000 (small condenser measurement mic) - omnidirectional

  • From: Wien
  • Registered: 2007-05-01
  • Posts: 99

Re: Analysing PWM/brightness induced noise of a TFT display

Digicheck will not do this.  You need a program that will do FFTs.  I use Cool Edit Pro, now Adobe Audition, to do what you are trying to do; but there are undoubtedly other suitable programs out there.

Cheers,

david

Classical ambisonic surround recording: UFX, FF400, Alesis HD24, Edirol R-44/88, Samplitude ProX 3.

david-p's Website

  • Registered: 2008-01-01
  • Posts: 3,025

Re: Analysing PWM/brightness induced noise of a TFT display

I tried using the Spectrum Analyzer of Ableton Live 7, but didn't get any meaningful readings yet.

  • From: France
  • Registered: 2007-09-14
  • Posts: 113

Re: Analysing PWM/brightness induced noise of a TFT display

Download from Voxengo their powerful and free VST plugin SPAN
http://www.voxengo.com/product/SPAN/
You just need then to record a piece of your noise through your DAW (hope it's VST compatible), enjoy SPAN an FFT tool as much accurate as my industrial sound analysers
Give a try to other Voxengo products by the way cool

HDSP9632, HDSP9652, ADI-8QS, FFUC, Quadmic II

5 Reply by Timur Born (edited by Timur 2008-06-09 22:29:53)

  • Registered: 2008-01-01
  • Posts: 3,025

Re: Analysing PWM/brightness induced noise of a TFT display

Thanks for the suggestion. I will have a look and try. I'm still not sure wether any of my mics records the signal at all. Let's see what the measurement returns.