aviorrok wrote:Recently I hear a noise sound at my studio around 10-15 Khz, when I'm using EQ the analyzer show there has a 20Khz "stand noise". How can I find the cause and "kill" the noise sound. I'm using UPS, TV, PC, UR242.
I'm not clear what the source sound is in your plot above? Is this the output of a microphone recording, or something else? In other words, is the ~20kHz tone from an acoustic source, or something being generated inside the audio equipment itself?
Assuming the former, and taking on board all that the others have said about possibly misleading displays etc, I would say that it's not that unusual to have high pitched whistles in studios and control rooms these days. I had hoped they would have gone away after the demise of the cathode-ray tube -- I was very sensitive to the 15.625kHz line whistle of UK TVs... But potential sources now include the power supplies and high-frequency inverters often used in the fluorescent backlighting of computer screens and TVs, as well as line-lump and internal switched-mode power supplies.
Inevitably, because they tend to oscillate at such a high frequency (typically 15kHz up to 40kHz or so) they can be very hard to track down with your own ears! However, I have had some success locating elusive HF whistles by using a handheld 'bat detector'. In my case a Ciel CDB101, and although I don't think that model is available any more, there are many other similar affordable devices on the market.
These devices use heterodyne technology to pitch-shift ultrasonic sounds down into a more easily audible range. (Bats use ultrasonic clicks and squeaks to echo-locate, of course). So, by turning the sensitivity down on a suitable bat-detector and moving it slowly around in your control room as you adjust the frequency knob, it is often possible to identify numerous ultrasonic whines and whistles coming from all manner of equipment!
Of course, having tracked down any culprits your options are usually pretty limited when it comes to dealing with the noises since replacement of the offending equipment is often not practical. Sometimes re-orientating the device helps as the noise emissions are often quite directional, especially with line-lump PSUs. Alternatively, you can make simple acoustic covers for the relevant items (being aware of any potential heat/fire risks, of course). Given the ultrasonic nature of these sounds, it doesn't take much in the way of a foam-lined baffle to reduce the radiation of unwanted noise dramatically.