Hunting high-pitched noise in the lab - Page 1
Forum section: electronics / testgear

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: September 19, 2021, 03:49:35 pm
content: On this forum, regularly people talk about noise coming from devices in their lab, like hum, noise from the fans, etc. Lately, I have been annoyed by some of my devices producing very high-pitched, audible noise. In this video, I hunt the suspects and analyze the noise they produce.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 19, 2021, 04:10:23 pm
content: Just named another beeping device in another threadThe FNIRSI-1013D. Turn down the brightness and there it is. Not sure about the frequency but it will be up high near what you measured from your power supply. My hearing is still very good and above what is normal for my age

author: james_s
author_rank: Super Contributor
timestamp: September 19, 2021, 06:19:10 pm
content: I have an audio spectrum analyzer app on my phone that I've used for this sort of thing. At my age I can no longer easily hear much over about 15kHz but I remember when I was a kid the whistle from the horizontal deflection on some CRT monitors would just about drill a hole in my head. I remember one of my highschool teachers being mystified that I could walk into the classroom and say that someone had left one of the monitors on in the video production station, she was an older lady and had no idea how I could tell but I could hear the whine from out in the hallway.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: September 19, 2021, 06:29:31 pm
content: QuoteWhich one? I use the iOS app "Analyzer" from dspmobile.com, a very capable app in many ways to measure sound level (with the proper selection for A/B/C weighting and various responses, 'semi-calibrated' for various iPhone models, and more). You need to pay a fee but it's worth it., It also has a spectrum mode, but I found the 10kHz to 20kHz range was made up of only 2 measurements so I went to look on.l..QuoteCertainly recognize thisI could also tell upstairs whether the TV downstairs was on or not. I live in The Netherlands (PAL 625 lines standard), so the line frequency tone there was 15625 Hz (625 lines × 50 Hz ÷ 2 because of interlacing).I see you are from the US, so that must have been NTSC. What is the line frequency for that standard?

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: September 19, 2021, 10:30:45 pm
content: Quote from: RBBVNL9 on September 19, 2021, 06:29:31 pmThe open sourceOscilloscope appis excellent for this application, as it has a precise spectrum analyser with near-real-time refresh rate (much quicker than in the video). I've also used its oscilloscope mode to calibrate engine RPM. May only be available from the open source F-Droid app store though.

author: 25 CPS
author_rank: Frequent Contributor
timestamp: September 20, 2021, 02:19:14 am
content: Quote from: james_s on September 19, 2021, 06:19:10 pmOh brother, I hate that sound. When I was in school, I could hear it whenever someone turned on a Commodore 64 from across the room because of the ear piercing whistle their monitors made. It was just painful hearing the horizontal oscillator start up knowing I'd have to endure hearing the screeching from it for a good chunk of the rest of the day. I didn't like the sound of it from television sets either but for some reason, the Commodore monitors were the worst.

author: Cubdriver
author_rank: Unknown
timestamp: September 20, 2021, 04:44:26 am
content: Quote from: RBBVNL9 on September 19, 2021, 06:29:31 pmThe horizontal oscillator frequency of 525 line NTSC television in the US was 15.75 kHz.-Pat

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: September 20, 2021, 01:31:44 pm
content: QuoteAh, right. First I thought it might be lower (as you had fewer lines), but then again the refresh frequency is higher so that compensates. So,for PAL it is 625 lines × 50 Hz ÷ 2 interlace = 15.625 kHzfor NTSC it is 525 lines x 60 Hz ÷ 2 interlace = 15.750 kHzThis siteoffers some more detail, also on sub-standards.Young people (including my students ;-) almost invariably will be able to hear 15k tones from TVs but also from other sources like faulty switched PSUs. Older people may not always hear them, but some certainly do.

author: james_s
author_rank: Super Contributor
timestamp: September 20, 2021, 07:23:23 pm
content: It's close enough that many NTSC displays will lock to a PAL signal, although there is usually not enough range in the user controls to properly size and center the picture, and the color encoding is completely different so you will only get B&W.Several years ago during a boring meeting I played with a tone generating website, it was funny to see the youngest guy in the room start looking around trying to figure out what the sound was that nobody else could hear.

author: TimFox
author_rank: Super Contributor
timestamp: September 20, 2021, 07:34:43 pm
content: Interesting, though pedantic, detail: PAL line rate is indeed 25 x 625 = 15,625 Hz, but NTSC is (59.97/2) x 525 = 15,742.13 Hz, although the previous monochrome rate was, indeed, 30 x 525 = 15,750 Hz. You would need very perfect pitch to tell the difference by ear, but the NTSC rate allowed a "hum bar" to move slowly up the screen at a beat rate related to (60 - 59.97) Hz.

author: james_s
author_rank: Super Contributor
timestamp: September 20, 2021, 10:07:11 pm
content: Those hum bars are a frequent nuisance in old arcade games, it's a common problem with PacMan and several others that used roughly the same design, fuse holders and edge connectors would develop high resistance and (I suspect) cause a ground loop.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: September 22, 2021, 12:13:45 pm
content: QuoteInterestingly, vector graphics-based arcade games would not suffer from this; they wrote polygons on a screen very much like a CTR oscilloscope writes XY plots to the screen. Some argue (probably right) that these had superior graphics and play compared to pixel-based systems those days. There was even a home system, called Vectrex, rather unique! It was short-lived, however; it required special screens and the Vectrex was built around a surplus of hospital heartrate monitors bought for a very low price. Once that stock was used, it was uneconomical to make more.

author: james_s
author_rank: Super Contributor
timestamp: September 22, 2021, 06:07:51 pm
content: Quote from: RBBVNL9 on September 22, 2021, 12:13:45 pmYes I have a whole collection of Atari vector arcade games so I'm very familiar with those. I completely agree that the graphics were superior to pixel based systems of the era, Asteroids for example has a resolution of 1024x768, impressive for 1979. It uses a digital vector generator with counters driving DACs so the concept of resolution does make sense despite not using pixels in a traditional sense. The later Atari vector games used an analog vector generator so they offer a higher theoretical resolution however the color ones are limited by the stripe pitch of the CRT.I've also worked on several Vectrex machines and am familiar with the hardware they use. I've never heard anything about a relation to hospital heart monitors and can see nothing to suggest any connection there. The Vectrex uses a standard off the shelf 9" B&W CRT with magnetic deflection. The deflection yoke is wound such that the veritical coils are substantially fewer turns than is used for a typical raster display and the deflection amplifier is built around an ordinary monolithic audio amplifier IC. The Vectrex was a victim among many others of the great video game crash that occurred in 1984, caused by a combination of a market saturated by too many low quality offerings from scores of different companies and the natural waning of the fad as the initial novelty of video games wore off. Due to the fact that the Vectrex was a self contained machine with its own display it was always expensive, and the monochrome aspect made it challenging to compete with systems using ordinary TVs that were cheaper and offered color graphics.

author: RBBVNL9
author_rank: Frequent Contributor
timestamp: September 22, 2021, 06:13:49 pm
content: Dear james_s, thanks for the reply!QuoteI read thathere. But then again, that source might be wrong, can't tell for sure...And yes, vector-based CTR is very very elegant. Wish there is (was) more of that...