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I have a friend which helps children with speaking disabilities, and she needs some software that shows the amplitude of the sound immediately as the children speak through the microphone.

I have tried Audacity, but it has a delay of about one second.

Any recommendations on such software?

Note that the OS is Microsoft, and the software should preferably be freeware.

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Just amplitude or the whole spectrum? –  slhck Aug 17 '11 at 19:32
    
Just amplitude. –  Claudiu Aug 17 '11 at 19:48
    
If you really want spectrum analysis then there is a trade-off between using a large window for the FFT (which gets precision and wide band at the cost of delay) and responsiveness. –  dmckee Aug 17 '11 at 22:30
    
If latency is an issue you will be better off with a sound device that supports ASIO - you can get a USB device with a couple of mic inputs for about $150 - if you really want zero (almost) latency between mic and screen this is the only way to go. –  BJ292 May 30 '12 at 19:41
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6 Answers

sndpeek

No idea if this is any use for you - it's Open Source:

http://soundlab.cs.princeton.edu/software/sndpeek/

enter image description here

sndpeek is just what it sounds (and looks) like:

real-time 3D animated display/playback
can use mic-input or wav/aiff/snd/raw/mat file (with playback)
time-domain waveform
FFT magnitude spectrum
3D waterfall plot
lissajous! (interchannel correlation)
rotatable and scalable display
freeze frame! (for didactic purposes)
real-time spectral feature extraction (centroid, rms, flux, rolloff)
available on MacOS X, Linux, and Windows under GPL
part of the sndtools distribution. 

SFS/RTSPECT

Just found this too:

http://www.phon.ucl.ac.uk/resource/sfs/rtspect/

Windows Tool for Real-time Waveforms & Spectra

RTSPECT is a free program for displaying a real time waveform and spectrum display of an audio signal. With RTSPECT you can monitor the waveform and spectral shape of sounds being played into the computer's microphone or line input ports. RTSPECT can display one or two-channel audio signals.

enter image description here

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Thanks! I think this sort of thing was what my friend was looking for. –  Claudiu Aug 17 '11 at 19:51
    
Nice find, especially because it's open source. +1 –  Randolf Richardson Aug 18 '11 at 0:16
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Audacity does allow you to monitor the input from the mic without recording. Don't know if this would reduce/eliminate the delay you experienced, though:
"either select "Monitor Input" from the input meter's pop-up menu, or else just click on the input meter." http://audacity.sourceforge.net/onlinehelp-1.2/toolbar_meter.htm

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A few other options from this question, particularly useful if you need something with few dependencies and easy to modify:

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Using the Volume Mixer isn't enough (right-click the speaker icon in the taskbar and select "Volume Mixer")? It will show level meters for all sounds being played through the system, and should include microphones as well.

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Well, it works, but it's a bit small...the children need to see the levels big on the screen so it can motivate them to speak loudly. –  Claudiu Aug 17 '11 at 19:11
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There are always delays in software when you do this sort of analysis on a computer. Unless you're using a high-speed driver such as those included with the Creative Audigy or X-Fi cards which are tuned for real-time performance capabilities.

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Yes, that's true, but if the Windows Volume Mixer can show the analysis in real-time, I think other software could do that as well :) The problem with Audacity is that I need to record for it to show me the analysis, and I guess that takes a bit of time too. –  Claudiu Aug 17 '11 at 19:14
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Here's a commercial offering that I found in a quick Google search, which offers a 30-day trial download so you can try it for free first to determine if it meets your needs (you mentioned that there's a preference for freeware, but not that free is a requirement):

  SpectraPLUS - FFT Spectral Analysis System
  http://www.spectraplus.com/

enter image description here

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Thanks, I'll take a look at it. –  Claudiu Aug 17 '11 at 19:49
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