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Author Topic: App for audio feedback frequency detection (giving the EQ band)?  (Read 4599 times)

Bohumir Zamecnik

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App for audio feedback frequency detection (giving the EQ band)?
« on: September 21, 2013, 02:59:43 pm »

TL;DR: Seeking advice with building a visual audio feedback detection app for mobile devices.

Hi, my name is Bohumir and I'm a programmer and amateur musician. As a hobby project I'm building an application that detects and visualizes musical tones in real-time. I've realized that another app based on similar principles might be useful to sound engineers. So for curiosity I've started writing a mobile/tablet application that would detect when audio feedback occurs on the live stage and what's the feedback frequency(ies). This in turn might help the sound engineer (SE) manually turn down the corresponding band(s) on the EQ. And I'm wondering if anyone else is interested in this problem. I'm asking myself the following questions regarding the fight with feedback and I'd like to ask you for advice.

 1. Does the frequency need to be detected exactly or just seletecting its corresponding EQ band is sufficient and more interesting?
 2. Is for less experienced SEs detecting the corrent band by ear hard (neither fast, not precise) and more more experienced ones a lot easier?
 3. Does even for experienced SEs detection by ear get worse if they're tired after many hours of work and/or would they like to confirm his guess by an exact measurement?
 4. There exist some general purpose real-time spectrum analyzer hardware units and mobile app. Do you thing a specialized app that would directly tell you the corresponding band on your EQ (in addition to the precise frequency) would be more beneficial?
 5. Also there exist some expensive hardware feedback eliminators that automatically adjust the EQ on your behalf. Many people tell that they are too aggressive in killing feedback at the expense of making the sound too dull. Do you thing a more lightweigtht and not fully automated thing like a mobile app could serve better?
 6. Do you thing that maintaining the list of feedback frequencies that occured during the live performance (eg. after the initial setup) would be useful? Eg. to quickly eliminate any of those if it occurs again.
 7. Is it important that the feedback detection distinguish feedback squaks from ordinary instrument and voice tones so that the music tones are not regarded as feedback?
 8. Is the almost real-time responsiveness (eg. delay of just several milliseconds) really important?
 9. Do you think that it is critical that the app just gets along with the built-in microphone or connecting to an auxiliary audio outout from the mixing console is not a problem?
 10. Would a phone or a tablet with bigger screen be better suitable for such an app? Or it doesn't matter?

I'd be very grateful if you could look answer or just discuss any one of those questions. Besides you raise your karma I could provide you with the application since the early development and fine tune the hand-crafted app to your specific needs. Overall feedback detection seems to be quite an interesting problem to solve and I'd be glad to hear if such an app helps saving somebody's time or maybe even a live performance :)

Thanks a lot!

Bohumir
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Mac Kerr

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« Reply #1 on: September 21, 2013, 04:01:14 pm »

TL;DR: Seeking advice

Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions in the Forum Announcements section, and on the registration page when you registered.

Mac
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Ivan Feder

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #2 on: September 21, 2013, 05:32:55 pm »

Already exists!
Audio kit app
« Last Edit: September 22, 2013, 07:45:52 am by Ivan Feder »
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Samuel Rees

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #3 on: September 21, 2013, 05:37:57 pm »

I use an iPhone App called "Octave" for this. I select 1/6 octave resolution so I can see more detail than a 1/3 octave EQ, but the 1/3 points are still on my graph.

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John Halliburton

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #4 on: September 21, 2013, 08:28:12 pm »

I've been using an app called "Frequency Finder", by Sonoma Wireworks.

The display is numerical, and when a feedback frequency is detected, it locks on it.  Quick, dirt simple, and cheap or free.

Ringing out monitors is pretty easy, you can drive the system just into feedback, see the first frequency, notch it, rinse and repeat to your heart's content-or to good engineering practices. ;>)

I typically just go to 1/6 octave on my Protea for the filter Q, and it's been working out great.

Best regards,

John

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Scott Middleton

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #5 on: September 23, 2013, 10:58:41 am »

do you have a link for Frequency Finder?  i couldn't find it on google or Sonoma's site.
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Sean Thomas

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #6 on: September 24, 2013, 08:32:45 pm »

To the OP,

There are many FREE and paid iOS apps that do what you are trying to do.  I can't imagine the need for another APP unless you were able to
do something different than what's out there.

I would "learn your competition" first by downloading all the apps and do some R&D.
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Bohumir Zamecnik

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #7 on: September 26, 2013, 03:40:38 pm »

Thanks people for replies! All of them are valuable. On the other hand, I'd like to specify what the app ought to be doing since it I'm afraid is could be misunderstood. The main differences to a plain spectrograph are the following:

  • Detecting frequencies of feedback (during its onset and course) among the signal and discriminating them with normal musical tones (to prevent false positive alarms).
  • Detecting the frequencies precisely. Not just to the nearest 1/3 octave bin or FFT bin, but to 0,0001-1 Hz. Also giving precise frequencies in the low-end (basses) - eg. up to 10 Hz. The purpose is to giving precise data for setting parametric equalizer (if needed) and to get good data for recognizing feedback among musical tones reliably.
  • Detecting multiple such frequencies at once.
  • Giving the sound engineer a (graphical) hint which band on a graphical equalizer to manually set based on the frequency so that he can reduce the reaction time. The particular equalizer type could be selected beforehand.
  • Maintaining a overview of feedbacks that have been detected and suppressed during the whole show.

I've looked at many applications out there that could possibly do the task, but none of them fulfills any of the requirements.

Please look at the attached images what kind of precision I'd like to utilize in detecting feedback frequencies - several examples of a prototype frequency detector under different conditions.

What do you think about it? Would you like that gun in your tablet/phone to help killing feedback? :)
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dick rees

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #8 on: September 26, 2013, 03:56:57 pm »


What do you think about it? Would you like that gun in your tablet/phone to help killing feedback? :)

I wish you luck with your design.  But for me, I'll just keep using my ears and experience.  I find that there's not really that much call for me to fight feedback if I have set up the sound system properly before the performance.  And if it should happen, I already know what to do about it.
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Dan Richardson

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Re: App for audio feedback frequency detection (giving the EQ band)?
« Reply #9 on: September 26, 2013, 04:13:01 pm »

My primary application for this would be during setup and soundcheck. I rarely have need for such a thing during a show.

  • Detecting frequencies of feedback (during its onset and course) among the signal and discriminating them with normal musical tones (to prevent false positive alarms).
  • Detecting the frequencies precisely. Not just to the nearest 1/3 octave bin or FFT bin, but to 0,0001-1 Hz. Also giving precise frequencies in the low-end (basses) - eg. up to 10 Hz. The purpose is to giving precise data for setting parametric equalizer (if needed) and to get good data for recognizing feedback among musical tones reliably.
  • Detecting multiple such frequencies at once.
  • Giving the sound engineer a (graphical) hint which band on a graphical equalizer to manually set based on the frequency so that he can reduce the reaction time. The particular equalizer type could be selected beforehand.
  • Maintaining a overview of feedbacks that have been detected and suppressed during the whole show.

Audio Kit, which is the spectrum analyzer displayed up above, does delineate the loudest frequency precisely, but doesn't do any of the other things on your list.

Multiple frequencies and the frequency history both seem useful.

Low frequency detection is obviously dependent on the input hardware. The iPhone analog inputs are pretty severely bandwidth limited.

Early discrimination without false positives seems like the big nut to crack.

Quote
1. Does the frequency need to be detected exactly or just seletecting its corresponding EQ band is sufficient and more interesting?
 2. Is for less experienced SEs detecting the corrent band by ear hard (neither fast, not precise) and more more experienced ones a lot easier?
 3. Does even for experienced SEs detection by ear get worse if they're tired after many hours of work and/or would they like to confirm his guess by an exact measurement?
 4. There exist some general purpose real-time spectrum analyzer hardware units and mobile app. Do you thing a specialized app that would directly tell you the corresponding band on your EQ (in addition to the precise frequency) would be more beneficial?
 5. Also there exist some expensive hardware feedback eliminators that automatically adjust the EQ on your behalf. Many people tell that they are too aggressive in killing feedback at the expense of making the sound too dull. Do you thing a more lightweigtht and not fully automated thing like a mobile app could serve better?
 6. Do you thing that maintaining the list of feedback frequencies that occured during the live performance (eg. after the initial setup) would be useful? Eg. to quickly eliminate any of those if it occurs again.
 7. Is it important that the feedback detection distinguish feedback squaks from ordinary instrument and voice tones so that the music tones are not regarded as feedback?
 8. Is the almost real-time responsiveness (eg. delay of just several milliseconds) really important?
 9. Do you think that it is critical that the app just gets along with the built-in microphone or connecting to an auxiliary audio outout from the mixing console is not a problem?
 10. Would a phone or a tablet with bigger screen be better suitable for such an app? Or it doesn't matter?

1. precise frequency is most useful.
2. Some people never get it. I certainly can't tell if it's 1.1k or 1.2k, or 40 Hz as opposed to 45 Hz.
3. I love confirmation. I use a lot of narrow notches, and if it's 432 Hz, I don't want to be cutting 428.
4. Don't care about the band. I rarely use graphic EQs.
5. The only thing I will do with an automatic feedback eliminator is eliminate it.
6. Feedback history sounds like an interesting thing to look at.
7. Obviously.
8. Fast is good.
9. I use them both standalone and aux send.
10. For this app, I just want a handful of numbers, big enough to see laying on the console. I am the reason that the display number in Audio Kit is so big. He was just using the default character set, and I couldn't read it without picking up the phone, so I emailed him. I would say a bigger screen wasn't needed, as long as your font is large. In fact, finding a place for another dedicated app tablet at my usual FOH would be difficult.
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