Strange overtones in a recording

Edited: October 26, 2019, 4:38 PM · Hi all.

I have recorded my practice with an iphone 5SE (and it's built in toy microphone). Somehow the recording picked up some sympathetic overtones, that sound like someone whistling along my playing. The recording was not tampered with, sound was not altered - it's as raw as it gets.

Not everyone can hear them (even with good earphones), but I was wandering if there is a rational explanation behind this phenomenon.

I should point out that I was not in the center of the room and that phone was tilted, so standing waves should not be that obvious. The violin itself does not emit the whistling noises either. It must be something in the way this microphone picks the sound up.

Replies (4)

Edited: October 26, 2019, 6:04 PM · I think it may be one of those situations where more than one thing is affecting the sound. I can clearly hear the resonance of the room in the recording, and tilting the phone or standing somewhere other than the center of the room isn't really going to change how the room sounds, which in this case is not ideal. So the first thing I would try is to record in any other space and see if the phenomenon is repeated. I also hear what sounds like maybe a bit of distortion in the preamps of the microphone in the recorder, or at some stage in the signal path. If you can adjust the gain there, that might be a thing to try. Or move the unit further away from you, and maybe try above the violin rather than underneath from the side. There's a harshness to the microphone sound that is what you can get from a small-diaphragm condenser mic, especially if it's too close to the violin. If I close-mic a violin, I generally use a ribbon mic for that reason. Still, you sound good, and I will listen to solo Bach all day.
October 26, 2019, 7:28 PM · Look up "comb filtering". You might have a bit of that, moving. Or not...
October 27, 2019, 1:53 PM · I don't hear whistling with my 70 yo ears, but in the past I have had harmonic distortion from a built-in mic, especially in double stops.

Also, a phone recording probably uses mp3-style compression, which can produce whistly "artefacts" if the bitrate is is low and/or fixed.

October 27, 2019, 4:24 PM · @Paul
I am aware of all the unfortunate parameters, like room modes (untreated) and the inferior mic and preamps. This recording was mostly just a test to see my general posture and facial expression, so I did it in my living room. I’d go to a studio and use a proper mike without the automatic compression and such. The harshness is there for sure, but this whistling thing blew me away. Never heard anything like this.

Comb filtering will usually occur when 2 sources of sound at a parallax create dips and bumps at certain frequencies. The harshness of the recording might be the result of sound bouncing off untreated walls, creating comb filtering. However - I do not believe extra sympathetic overtones are caused by that.

I do not know what iphone uses, but upload to a website reencodes the sound, taking some of that sympathetic whistle away (not adding to it). Probbably cutting away “frequencies humans do not hear”. (Yeah, right)... but you are right. This appears at chords and double stops, but somehow continues for a while after.

I’ll go to the studio and make proper recording (just to make sure the fiddle is not the culprit). But Sinceely - do not hear this while playing it. But then again, this violin is so loud, I hardly hear anything after... :)

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