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[frank kayser]

Hi folks,
Last night when mixing on the Cafe's system, the trumpet player said she heard some ringing - maybe attached to the reverb. So I backed down the total amount of reverb, and it was still there.  Knocked the HF of the reverb down 20db. Still there.


Round and round I went - channel by channel - sometimes I could hear it, many times not. The trumpeter is roughly half my age, with what I believe may be perfect pitch - says she drives her piano tuner to drink.


Finally, I remembered I had AudioTools on my phone - and the SMAART application.


Looking it at 1/24th octave, I noticed a recurring spike roughly 16khz.


It was a four piece all female band with 4-part harmonies, trumpet (not mic'd), electric guitar, also un-mic'd, Bass, also un-mic'd and a drum kit consisting of a snare, a number of cymbals, and a cajon with a kick pedal, equipped with a piezo, triggering a drum module hooked into the PA. The bassist doubled on an acoustic piano w/Helpinstill pickup system and vocal mic.  In summary, 5 vocal mics, the cajon as bass drum and piano in the mixer.


Back to 16khz repeating "blip".  I made more adjustments to pull as much 16k and above out of each channel. Still persisted.  Changing to 1/48th octave, the peak showed closer to 20k than to 16k.
Muted the piano and the piano vocal mic to no avail.  Muted each channel singly, and no channel seemed to make a difference.  Even muting the drum vocal mic which was picking up the cymbals did not have an effect, and neither the cajon input.


I turned the tweeters down on the cabinets, and dropped the rack eq 16-20k down about as far as it would go.  Finally got the ring out (mostly, or at least to a point where it was not a problem.  Still a peak there, but 1/4 as large.), but now I had to figure out how to get intelligibility back.


The audience and the other musicians never heard the ring, nor did they detect (or at least comment on) my playing all night with the high frequencies.  Got quite a few compliments from the audience members, and hugs from the band.  Still...


I never did find the source.

I've never had that problem at the cafe (or these old ears never heard it).
Adjusting without knowing why is just like being a parts changer while claiming to be a mechanic.
Any ideas what may have been producing those "rogue" peaks?  I'm lost.

thanks in advance,
frank

[Michael Lascuola]

Wow - something that high, I wonder if it was electronic feedback -- not acoustic.
Was anyone wearing in-ears?

You mentioned "the Cafe system" -- can you bring your own mixer next time?

[Lee Douglas]

Maybe a send on an effects return channel ever so slightly open on itself?

[Tim McCulloch]

Hearing aid in the audience, steam leak in the espresso machine?  Since it didn't go away when you all but shut down the system, I'd say it wasn't a system issue.

[Ed Hall]

Hearing aid in the audience, steam leak in the espresso machine?  Since it didn't go away when you all but shut down the system, I'd say it wasn't a system issue.

This was my thought as well as I continued reading. You can’t fix what’s not in the system.
I’ve been there and it is very frustrating. The desire to know what and why can be very strong.

[Chris Hindle]

Hearing aid in the audience, steam leak in the espresso machine?  Since it didn't go away when you all but shut down the system, I'd say it wasn't a system issue.

I was thinking "Hearing Aid" also.....
Just last week I related a story about the DJ that left his mic on when the band took the stage... Took a few minutes to find his system feeding back, not mine.
Chris.

[Jay Barracato]

I was thinking "Hearing Aid" also.....
Just last week I related a story about the DJ that left his mic on when the band took the stage... Took a few minutes to find his system feeding back, not mine.
Chris.

While I haven't heard the hearing aid one other than as stories, I have been puzzled by whistling AC units and warning tones on fire suppression systems.

Sent from my Moto Z (2) using Tapatalk

[John Roberts {JR}]

While I haven't heard the hearing aid one other than as stories, I have been puzzled by whistling AC units and warning tones on fire suppression systems.

Sent from my Moto Z (2) using Tapatalk

I've seen (heard) the hearing aid event in real time. I was giving a talk to an audiophile group back in the 80s and some older gentlemans ear piece fell out. He was so deaf he didn't hear it... The guy demonstrating his high end audio system dived for the amp power switch trying to save his tweeters. 

Back to your story.. a 16kHz acoustic feedback path is very short. More common for noises that HF to be from external sources.

JR 

[frank kayser]

Thanks guys. You've pointed me in a totally different direction - That's wild! I wouldn't have ever suspected the IEM as a source of this particular problem.  Hearing aids?  Really? I do believe you, yet this is so far out of my knowledge, experience, and even imagination.  My mind is not wrapping around how.


Yes, I had Sennheiser IEM running on the moniyor bus; a wireless G3-500 bodypack sending to a Senn g3-300 IEM receiver.


It noise lasted all three sets - second set, there was a film crew there running a Sennheiser ENG unit off Aux 9/10. 


Now that we have a suspect, what may have been the interaction?  IM artifacts?  Proximity of the transmitter to the mixer?   How does that play with hearing aids"


Wow.

[frank kayser]

Wow - something that high, I wonder if it was electronic feedback -- not acoustic.
Was anyone wearing in-ears?

You mentioned "the Cafe system" -- can you bring your own mixer next time?

Yes. I had an IEM on the monitor bus.
I work at the cafe about 15 nights/month,  and was responsible for putting the cafe's system together.  I can easily substitute my A&H QU-Pac for their QSC Touchmix 16.

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