What's that sound behind the applause in the live opera broadcast?
February 3, 2018 10:56 AM   Subscribe

I like to listen to the weekly live (or recorded-live) radio broadcasts from the Met Opera. Whenever the audience applauds, there's a weird sound in the background - to me it sounds like alternating kinda high G and F# notes, 2 or 3 times per second, slightly irregular in timing. I've noticed this for months. What the hell is it?

I would've guessed it has to be some sort of artifact of their house microphones being overloaded by the applause - but then why is it two alternating notes instead of one constant sound?

I listen to the broadcasts on an ancient Bose clock radio / CD player, but I don't think it's the radio's fault, because I've never heard anything like this on any other radio or CD.
posted by moonmilk to Media & Arts (12 answers total) 2 users marked this as a favorite
Response by poster: Oops, to that last point, I meant to say "never heard anything like this on any other radio broadcast or on a CD."
posted by moonmilk at 11:15 AM on February 3, 2018

Hmmm...maybe it's the auto-tuning feature on your radio thinking it's gone all static-y and is moving up and down the dial trying to tune into a station it's already tuned to?
posted by sexyrobot at 11:40 AM on February 3, 2018

Response by poster: Interesting suggestion, sexyrobot! Since the opera is on now, I watched the little "STEREO" light on the radio that lights up when the signal is tuned in nice and strong. It didn't flicker during the applause just now, but I didn't hear the artifact this time either.

Maybe it's on to us.
posted by moonmilk at 12:00 PM on February 3, 2018 [1 favorite]

Have you tried listening to the WQXR live stream on your computer to see if the same things happen?
posted by duoshao at 12:04 PM on February 3, 2018

Response by poster: OK, this time on the radio I do hear the artifacts quite strongly but the STEREO light is steady.

On the internet stream, the sound is kind of muddy with very little high end, so I'm not sure whether the artifact is there or not! I'll keep listening to the stream and report back.
posted by moonmilk at 12:07 PM on February 3, 2018

Response by poster: OK, more observations.

It's really hard to hear on the internet stream, because the high end is so muddy, but I think it's still there. At one point I thought I could hear it an octave or so lower.

Here's a recording of the sound of my radio - the tones are most audible when the announcer is speaking. You can also hear my dog jingle his collar in there!

posted by moonmilk at 12:59 PM on February 3, 2018

Just tuned in long enough to hear the end of the live broadcast, and the effect you were talking about came through LOUD AND CLEAR — and this is through a $400 Yamaha amp and a decent set of speakers so I don't think your clock radio has anything to do with it. It was definitely louder while the applause was taking place, but when the applause died down and all you heard was room tone behind the announcer, the oscillating tone was still there, albeit much lower, mixed in with the ambience. As soon as the presentation kicked back to the in-studio DJ at WQXR the effect was completely gone. I didn't really hear it behind the Internet stream, but as you've noted it's not a great-sounding stream so it's hard to tell whether that means anything.

Anyway, to me this sounded like a digital compression artifact. Specifically, it sounded like a codec somewhere in the recording or transmission chain was getting all knotted up trying to resolve the ambient room noise/reverb inside the Met, maybe due to a highly restricted bit rate but also possibly due to some kind of filtering meant to shape the sound to allow it to be compressed more efficiently. CAVEAT: I'm no audio engineer, so this is not expert advice. But it does sound an unwanted (and perhaps easily corrected) digital artifact to me.

Since the Met Opera program is provided through something called the "Toll Brothers–Metropolitan Opera International Radio Network" my assumption is that either they're doing some funky (and thus ill-advised) compression before distributing the program to member stations, or (more likely?) WQXR itself is screwing something up when they rebroadcast the signal. The only way to check for sure would be to listen to the broadcast over another station to see if it's clean or if it has the same audio artifact. Maybe you should contact listener services at WQXR to be sure they're aware of it.
posted by Mothlight at 1:18 PM on February 3, 2018 [5 favorites]

Response by poster: I'm glad to know it wasn't just me!
posted by moonmilk at 1:37 PM on February 3, 2018

I hear it too, especially on the Sirius channel, and I always assumed it was a digital compression artifact of the high-pitched sounds generated by applause. /notanaudioscientist
posted by matildaben at 6:04 PM on February 4, 2018

I'm probably gonna change my answer to 'compression artifact' as well. Think of youtube video...say, a scene of two people talking. Youtube 'frames' aren't like movie frames where each frame is an entire image...it's more like 'keyframes' and then 'alterations'. So, in the example, the first frame is of the entire image of the two people and all the subsequent 'frames' are just the lips/eyes/hands/whatever actually changes that gets overlayed on the original image. The entire image doesn't change until the next shot (cut to: beach scene) and thus the data transfer is kept really low...unless things are changing/cutting too fast and then you get stuttering or artifacts. The 'worst case scenario' for this algorithm is...old-style TV static, because every pixel is changing constantly. Another way that youtube keeps stuttering down (when too much is changing) is to apply JPEG-style compression to the moving parts, making them blockier/chunkier, but keeping the data level down.
In audio, sounds are composed (like other colors are made from the primaries) by mixing together several kinds of waves (square, sawtooth, and triangle if you're interested...which are in turn made from combinations of sine waves), and 'noise' AKA 'static'. Same kinda deal as above with some changes...the waves can be modeled mathematically, the static, not so much. Applause is enough like static to trigger the JPEGy compression, or just having drop-outs that allow more of the wave sounds to come through.
Either that or the flute player is just messing with you during the breaks. ;)
posted by sexyrobot at 7:29 PM on February 5, 2018

Response by poster: Update: it happens on their Live from Carnegie Hall broadcast too, both streaming and FM radio.
posted by moonmilk at 6:48 PM on February 23, 2018

Well...even on FM, these days I highly doubt that any transmission doesn't spend at least some time being digital between the microphone and your radio, even if it's just in the 7-second-delay machine (so they can catch and bleep swear words--required by the FCC). My vote is still for 'digital artifact'
If you really want to hear this effect, try recording it digitally, but use a really low bitrate...it should really stand out as musical/warbly instead of static-y/hissy.
posted by sexyrobot at 8:51 AM on February 24, 2018

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