High pitched noise on USB mic recordings

Have just bought an old Editors Keys SL600 studio mic, early black version, and this works fine monitoring on the headphone jack on the mic but if I try to click ‘start monitoring’ I get a high pitched noise through the headphones similar to when you phone a fax machine up. This happens when ‘record’ is clicked but is only just audible when playing back the recording. Have looked at all the settings and gone through the manual without success. The mic headphone monitor has also a quite loud hiss but this is not transferred to the recording. The mic was bought so that my sister could record some poetry and seemed ideal for the job and only cost £13.50 from Ebay. The voice recordings are pretty good but the high pitched noise is a problem. Is this a fault with the mic or a setting up problem with audacity. I love the program and while I have been in electronics all my life, now retired, I have done very little in audio. Hope someone can help

I know this isn’t likely, but do you like to record things from the internet? The settings for that tend to mess up live recordings.

Audacity > Edit > Preferences > Devices > Recording.
Do you see your microphone there – or something that reads like “USB Audio Device,” Or possibly the name of your microphone.

So to recap, you get a serious whistle during live recording, but while the exported show has the whistle, it’s nothing like during the performance?

Can you post a little of the whistling performance here?


Also include a brief section with no voice at all – just silence.


but is only just audible when playing back the recording.

First, make sure it’s a recording problem, not a playback problem.

I suggest you leave the first 30 seconds or so of the recording as-is to make sure you are “testing” at the normal playback volume. Then mute the audio (Edit → Remove Audio → Silence Audio) and see if the noise is gone. If the noise is gone, the problem is in your recording. If the noise is still there, it’s coming rrom your soundcard at playback-time, and if you play it back on a better system it won’t be there… .

How are your levels? Typically, you’d like to have peaks around -6dB in the digital recording. You’d like to get close to 0dB, but if you “try” to go over 0dB, you’ll get cliping (distortion). If she’s not close-enough to the mic, or she doesn’t speak with a strong voice, you’ll get a weak signal. That results in a poor signal-to-noise ratio (and when you boost the volume in post-production or at playback time, you’ll boost the noise too). You do want to make sure you’ve selected the mic, and the mic only as your recording source (not “Stereo Mix” or What-U-Hear).

There is always some analog noise. With a good mic & preamp, the acoustic room-noise is usually stronger than the preamp noise, even in a soundproof studio. In your case, the noise is probably coming from the mic’s internal preamp (probably with the preamp picking-up noise from the digital USB signal, or from the USB power.) Once the signal is digitized (inside the USB mic), no noise will be added. The computer & recording software should have no effect on the digital “audio data” at all!

That’s why you want to be really careful about your description of the problem. Gentle, rain-in-the-trees-hiss is perfectly normal for a microphone preamplifier. They all do it and the lower that number is, typically the more expensive the preamp.


Thanks for the replies. I have silenced the audio as suggested and the noise ceases so it is the recording device. The high pitched noise is at quite a high volume when making the recording and listening via the headphone jack on the mic but playing back the recording the high pitched noise is 10 or 20 times lower in volume but still audible. I think it is the mic picking up the USB signals and have contacted Editors Keys for advice. I tried running the mic through windows ‘sound recorder’ with the same results. The fault is probably some of the small surface mount electrolytic capacitors have dried out and need replacing which is something I can do. The sound from the mic is excellent so I would love to get it working like it should.

Hi Again this is a short recording of silence for few seconds to show the whistle.

That definitely sounds like electrical interference.
If you are on a laptop, it may be due to the power supply. Try running on batteries while recording.

If you are on a full size computer then it is likely to be noise on the USB supply. In this case, attaching the USB microphone via a powered USB hub may help, but note that it is not recommended to share a USB hub between a recording device and another USB device (that can cause other problems such as drop-outs and crackles) so if you try a USB hub the microphone should be the only device using it.

Also try switching off other electrical equipment in the house (including lights) just in case the interference is from an external source.

This is really tiny stuff. Try two notch filters.

Effect > Notch Filter:
Freq: 278, Q:5
Freq:1007, Q:5

Or try one at a time and see if one whistle is worse than the other. These filers may affect the sound of the show.

These two tones are present in really tiny amounts in the sample you sent. I do wonder how you heard it. Do you have to crank the volume up during the playback? Are you making a proper recording? Do your red recording meters peak between -6 and 0 during the show?

You can make your meters very much larger to help with this.


Click on the right-hand edge of the meters and pull sideways. Large meters are highly recommended.


Thanks for the replies guys. The level was set so that a quiet voice recording was normal at about 30cm from the mic. I did do a voice recording plus the silence but it was too long to upload so I used that one. I will agree it is not loud but it can be heard above quiet passages of speech. Also it is 100 times louder through the headphones when monitoring the speech. Being an electronics engineer all my working life I had a look inside the mic today and think it is something to do with the 40v supply to the condenser transducer. Contacted Editors Keys and they are going to have a look at it for me and give me an estimate for repair, if possible. I can drop it off in Manchester as I live close and can go by bus and use my bus pass to save money. It’s a beautiful mic and I would love to see it fully working again.

I had a look inside the mic today and think it is something to do with the 40v supply to the condenser transducer.

Maybe. But you have to account for the difference in effect between the live recording and the later playback. If I had to guess at it, I’d say the 40v element supply is very highly filtered and regulated. It has to be in order to work at all.

The straight microphone preamp, line amplifiers and A/D converters may be working from the unfiltered 5v from the computer. Goodness knows what kind of garbage that can inject.

You can do one trick. If you have a wall-powered USB hub, connect the system through that into the computer. The 5v to the analog electronics is now coming from the wall socket instead of the noisy computer. You may not connect anything else to the hub when you do this.

Noisy 5v getting into USB-powered electronics is very common.


I did suspect that the 5v supply was the culprit so used my oscilloscope on the 5v input to the mic and also after the filter in the mic and there was no real interference more than a few millivolts in there. There were two decoupling capacitors that normally I would have replaced if I had the tackle to do it but the mic is now back at Editors Keys for a free estimate of cost to repair it.

Do write back if/when the problem is resolved.

Just an update in my Editors Keys SL 600 mic problem with the high pitched data noise on it. I have got the mic working with just the 5volts from the USB port and not the data connected as I blew the codec IC. Have ordered a new IC and will fit it soon but Editors Keys contacted me and said they have a fully working Mk 2 SL600 mic that I can have for free as they can’t sell it. Mine is a Mk 1 version so the Mk 2 should be brilliant I am gobsmacked at this and look forward to playing with a working mic. Cheers malc

Will post again if I cure the Mk 1 mic I have and also report on the Mk 2 model when I get it. Malc

If you can’t prevent this whistle it can be notched-out using Steve’s Code below in Nyquist Prompt.

    (setq mysound s)
    (setq q 10)         ; set the base Q for the filter
    (setq iter 15)     ; set the number of iterations
    (setq freq 1000)  ; set base frequency

    ; start the DO loop
    (dotimes (i iter mysound)   
    (setf mysound (notch2 mysound (* freq (1+ i)) (* q (1+ i))))
    )                     ;end of loop

Well after a lot of faffing about I finally have a solution. The Mk 2 SL 600 that Editors Keys gave me was very low output so they gave me an SL 150 that is fine. The old Mk 1 SL600 does not work on USB any more but has been kept as it does have the same capacitor diaphram as the SL150 so may come in handy for spares or I may modify it to a basic non USB mic. So far the only problems I am encountering are cutting the noise from the fan on the PC that is being picked up by the mic, but this is being discussed on another thread on here and is close to a solution.