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I would like to record specific audio for the following scenario. I have a piece of equipment that rotates a drum via an electric motor. The drum contains food product that is heated by air entering the drum. The food inside the drum cracks very lightly when it is fully cooked. The problem is that the cracks are audible, but barely. The whine of the motor and inflow and outflow of air is drowning out the audible cracks.

I figured a solution would be a certain microphone that would concentrate it's sensitivity close to the drum, therefore avoiding all the background noise. Unfortunately I am NOT an audio expert in the least. What microphone would work for this setup? Any other tips with how to filter the microphone and process the audio in real time.

I am a computer programmer so designing software would not be an issue for this. I mainly need help picking out hardware and fully understanding the problem domain so I can design a solution. Below is a youtube video of the equipment.

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2 Answers 2

There are probably many different solutions to this problem. One thing you don't need to do is write more software. There is plenty of great software out there that will do the job. Hiring a local audio engineer who has experience with sound design and recording will probably save you a lot of time, money, and headache.

But if you want to do it yourself, or know what to look for, here are two ideas:

  1. Process recordings of the actual device to get the desired sound.
  2. Make recordings of similar things and assemble them together so that they make the sound you want. (Foley)

It may help to use one or more shotgun microphones to record your device. You probably won't be able to perfectly isolate the sound you want this way, any more than you would be able to take a picture of a perfect sine wave in a bathtub that contains a toddler - no matter how expensive the lens you buy.

You may be able to do some filtering to remove unwanted sound - Audacity either includes all the filtering tools you need, or the separate plugin bundle does. You may also want to look into FFT audio editors such as SPEAR. This isn't easy, though. It will take time, reading, and practice to build the basic skills you need. And then more time and practice to actually extract the sound you want.

In movies, TV and commercials a process called Foley is used. Foley work is basically recording things that sound similar enough to the sound you want, and then dubbing them together to make a soundtrack. Many of the "realistic" sound effects we are used to hearing are just as fake as the 3D graphics we see. In some cases, we are so used to the fake movie sounds that the actual sounds in real life sound "fake".

You might be able to get the sound you want by baking your stuff on a cookie sheet, and then pulling the cookie sheet out and holding a microphone up against the cooling stuff. Then you overlay that sound on top of the blower sound of your machine before it starts popping. If that doesn't work, try other household goods that make the right sound. If that doesn't work, go crazy at the supermarket and hardware store buying likely items to smash when you get home.

TL;DR A Shotgun Microphone is the piece of equipment that you think you want, but equipment alone won't solve this problem.

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Mainly I would like the audio processed in real time so I can listen with headsets and/or have a visual representation of the audio signal before/during/after the cracks start. Technically, recording would be nice but is optional. I need to do this realtime –  ctilley79 Jun 9 '13 at 2:06
    
Then you probably will need a high quality shotgun mic, microphone preamp with phantom power, and a parametric EQ. There are plenty of parametric EQ solutions in software. –  ObscureRobot Jun 9 '13 at 21:21
    
Can you recommend a specific mic around 100 or so bucks? –  ctilley79 Jun 9 '13 at 22:53
    
AVP is not for shopping recommendations. Go check out B&H and see what they offer in your price range and then google for reviews. –  ObscureRobot Jun 10 '13 at 0:17
    
This is even worse than stack overflow ;) –  ctilley79 Jun 10 '13 at 1:30
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Tell me if I'm wrong but, I think you want to detect the point at which the foodstuff starts making the noises so that you can halt the process or time some other process from the instant they are making the noise.

I think ObscureRobot's answer assumes you want to make a recording of the noises that the food makes? Forgiveness please if I've misrepresented questions and answers here.

Anyway, it is likely that you can use digital or analogue filters to focus on the part of the spectrum the foodstuff noise occupies. Then you should be able to eradicate a lot of the background noise and have some form of "detector" to trigger the next process.

Like I say if I haven't got the idea correct, the same process to filter the sounds will be used even if you just want to record the sound made by the food.

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Mainly I would like the audio processed in real time so I can listen with headsets and/or have a visual representation of the audio signal before/during/after the cracks start. Technically, recording would be nice but is optional. –  ctilley79 Jun 8 '13 at 20:08
    
Mainly your idea is correct. Can you help me design a more specific solution? –  ctilley79 Jun 9 '13 at 2:07
    
You need to make a microphone recording of what is actually happening - start off with the regular noises of the motor and mechanisms so that these can be analysed in the spectrum to see how they will be removed. Then when the foodstuff noise comes in we'll want to accenuate their noises. But you'll need to find a microphone that can be fixed on the mixer somewhere and make a decent recording. I can analyse the recording. –  Andy aka Jun 9 '13 at 8:40
    
Can you make a microphone recommendation? –  ctilley79 Jun 9 '13 at 13:24
    
I can't make a suggestion other than use a small condensor mike and place it as close to the foodstuff sounds as possible. Make a recording and try and filter in what you want and filter out everything you don't want. –  Andy aka Jun 9 '13 at 13:54
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