Maximizing Your Sound System: Understanding FFT and Low Frequencies"

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Discussion Overview

The discussion revolves around the use of Fast Fourier Transform (FFT) to analyze sound frequencies produced by a sound system, particularly focusing on low frequencies and the challenges faced in obtaining clear sine wave outputs. Participants explore technical aspects of sound analysis, including sampling rates, noise filtering, and the impact of audio settings on the quality of FFT results.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant reports that their FFT is functioning for frequencies between 51.91 Hz and 7902 Hz, but notes confusion regarding the output for certain low frequencies, questioning if this is normal.
  • Another participant requests additional information about the sample rate and number of samples used to better understand the FFT results.
  • Participants discuss the importance of applying a taper before performing the FFT to improve results.
  • Concerns are raised about the presence of noise in the FFT outputs, with suggestions to plot more data points to visualize the waveforms better.
  • One participant mentions filtering out frequencies below a certain magnitude to reduce noise, prompting questions about the appropriateness of this threshold.
  • There is a suggestion to directly feed electronically sourced tones into the analyzer to eliminate ambient noise before using a microphone for real instruments.
  • Participants discuss the potential issues with reading stereo audio data as mono, which could affect the FFT results.
  • One participant expresses uncertainty about the settings for their microphone and how it affects the output.
  • Another participant emphasizes the need to address the noise issue in the data before applying FFT, as filtering after the fact may not resolve the underlying problems.

Areas of Agreement / Disagreement

Participants express varying opinions on the causes of noise in the FFT outputs and the effectiveness of the filtering methods employed. There is no consensus on the best approach to resolve the issues presented, and multiple competing views remain regarding the handling of audio data and settings.

Contextual Notes

Limitations include potential misunderstandings about stereo versus mono audio data, the impact of environmental noise, and the adequacy of the filtering methods used. Participants also highlight the importance of sampling rates and data visualization in achieving accurate FFT results.

  • #31
This is confusing. If you are dealing with the acoustic input from a microphone then what has the source data got to do with it?
I still don't know why you need to use acoustic connection. What's wrong with a double ended jack lead?
If you are using C, then you can surely extract alternate samples from any audio file you want to analyse. There seems to be a'big hole' in all this and I'm not sure what's missing.

It could help you and us if you were to draw a block / function diagram of what you are doing. There just has to be a straightforward answer to your basic problem.
 
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  • #32
Ok so

I am using a built in computer microphone. so there are no connect to be make.
sound1.jpg


And I am using a Dell Computer...

now my problem comes in with noise in my input ...
so there no noise in my room but I get this :
graph.jpg


and this is which
Math.Abs(F.Magnitude) > 300000
 
  • #33
You need to go right back to square one and check out each individual link in the chain.
If you record 'silence' and then a burst of high level 1kHz, what does the straight play back sound like? Noisy? Also, what does high level 1kHz look like when plotted on those two graphs ("my test graph")?
The make of the computer should not be important for this. If it has an internal microphone, does is have an identifiable sound card or does it not have 'slots'?
 
  • #34
ok here is how it looks:
mytestgraph.jpg
 
  • #35
You missed out the y-axis on the latest pics. but it looks ok. However, I wonder if you have just set the gain of the mic to auto and you are just seeing a scaled up version of the most recent pictures in the previous pictures.
You should find that somewhere in the options.
 
  • #36
ok sorry about the last pic:
mytestgraph2.jpg


now as for the setting of the Microphone there are not auto gain that I can see:
setting.png


listening.png

is there any other place I should look?
also do you know what Microphone Array does ?
wiki say's is it a "Systems for extracting voice input from ambient noise (notably telephones, speech recognition systems, hearing aids)"... and that is what I am trying to do..
 
  • #37
There must be some level control somewhere - that could still be your problem.
I have no idea about the "microphone array" but you could google PC Sound Control Microphone array.
I know the Apple user interface is very simple but limited (that's what I'm used to) but some of the Windows panels are total gobbledegook to me. I suggest you try the 'Levels', 'Configure', 'Properties' and you must find an audio input level adjust.
What software package is taking the sound into record it? Is there not a control there? The point is that the levels just don't seem to make sense. The noise seems to be higher on 'silent' than with the 1kHz - which implies some expanding is happening. Did you listen to the recording (on headphones or your friend's HI Fi) - you will need loads of Bass because the high level shash on your graph is all at 40Hz and below.

Your problem is that you are trying to do something sensible with some 'toy' kit for listening fun. Home stuff always falls short, one way or another. You just have to battle it out.

BTW, Microphone Arrays are used for directionality (as with radio antenna arrays). You have only one mike so I don't think that's relevant. I have two mikes on my deaf aids and one switch position claims to reduce sounds from behind. It uses a phase shift between them. It does work sometimes but never very well. Is that a tick I can see on the Mic Array setting on the control panel? I don't think that should be selected for serious stuff.
 
  • #38
ok i did not see any
 

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  • #39
I refer to the picture of the control panel in Post 36.
 

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