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POWhy does my FFT gives a different visualizer output than Windows Media Player?
 

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  1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
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    <p>I am trying to implement an audio spectrum analyzer in android using the <a href="http://developer.android.com/reference/android/media/audiofx/Visualizer.html" rel="noreferrer">Visualizer</a> class.</p> <p>I am getting FFT data in the <code>onFftDataCapture()</code> method of <code>OnDataCaptureListener()</code> event and I'm drawing that on the canvas using <code>drawLines()</code>.</p> <p>But the spectrum display is not showing properly. I can see changes on left side of graph only. But in Window Media Player, the output of the same song is different. What I am missing?</p> <p>Can anyone help me on this with an example or a link?</p> <p><strong>CODE</strong></p> <pre><code>mVisualizer.setDataCaptureListener( new Visualizer.OnDataCaptureListener() { public void onWaveFormDataCapture(Visualizer visualizer, byte[] bytes, int samplingRate) {} public void onFftDataCapture(Visualizer visualizer, byte[] bytes, int samplingRate) { mVisualizerView.updateVisualizer(bytes, samplingRate); } }, Visualizer.getMaxCaptureRate() / 2, false, true); </code></pre> <p><strong>onPaint()</strong></p> <pre><code> for (int i = 0; i &lt; mBytes.length / 2; i++) { mPoints[i * 4] = i * 8; mPoints[i * 4 + 1] = 0; mPoints[i * 4 + 2] = i * 8; byte rfk = mBytes[2 * i]; byte ifk = mBytes[2 * i + 1]; magnitude = (float) (rfk * rfk + ifk * ifk); int dbValue = (int) (10 * Math.log10(magnitude)); mPoints[i * 4 + 3] = (float) (dbValue * 7); } canvas.drawLines(mPoints, mForePaint); </code></pre> <p>Where <code>mVisualizer</code> is Visualizer class object, and <code>mBytes</code> is FFT Data got from <code>onFftDataCapture</code> event.</p> <p>You can read more about FFT data returned by event <a href="http://developer.android.com/reference/android/media/audiofx/Visualizer.html#getFft%28byte%5B%5D%29" rel="noreferrer">here</a>.</p> <p>This is what values I get <code>onFftDataCapture()</code> :</p> <p><code>[90, -1, -27, 102, 13, -18, 40, 33, -7, 16, -23, -23, -2, -8, -11, -9, -8, -33, -29, 44, 4, -9, -15, -1, -2, -17, -7, 1, 1, 0, 3, -11, -5, 10, -24, -6, -23, 1, -9, -21, -2, 4, 9, -10, -14, -5, -16, 8, 6, -16, 14, 3, 7, 15, 10, -2, -15, -14, -5, 10, 8, 23, -1, -16, -2, -6, 4, 9, -1, 0, 0, 9, 1, 4, -2, 6, -6, -6, 8, -4, 6, 6, -4, -5, -5, -2, 3, 0, -1, 0, -7, 0, 2, 1, 0, 1, -1, 0, -1, 1, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, -1]</code></p> <p>Any idea, link would be helpful.</p> <p><img src="https://i.stack.imgur.com/AcSPT.png" alt="Partial value drawing"></p> <p><img src="https://i.stack.imgur.com/LASMQ.png" alt="full value drawing"></p> <p><strong>Update for @Chris Stratton</strong></p> <p>Now i am playing <a href="http://en.wikipedia.org/wiki/File:Square_wave_1000.ogg" rel="noreferrer">square wave at 1000 Hz</a> file and took screen shot of that. What you suggest now?</p> <p><img src="https://i.stack.imgur.com/SFzMc.png" alt="1 KHz spectrum"></p> <p><strong>Updated after @ruhalde suggestion</strong></p> <p>Now I am playing <a href="http://www.burninwave.com/#freqsweep" rel="noreferrer">Frequency sweep (20-20000 Hz)</a> file and this file generated following output.</p> <p><img src="https://i.stack.imgur.com/gO6xz.png" alt="Frequency sweep (20-20000 Hz) output"></p>
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    1. USRajkishor Sahu
    1. USRajkishor Sahu
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
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    2. VO
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
      1. USChris Dennett
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    3. VO
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
      1. USRajkishor Sahu
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    1. COAre you clearing your canvas before each time you redraw the spectrum? I'm just (wildly) guessing the broken pieces are left over from previous draws...
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
      1. USGuy Sirton
    2. COI am calling `invalidate()` in `updateVisualizer()` method. It is doing that task.
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
      1. USRajkishor Sahu
    3. COI think your dB and magnitude formulas are not correct. First magnitude is calculate by multyplying with SQR(2). Also in dB you need to divide by a limit, as dB is always a measure related to something. You are not diving by your limit, so your limit is 1 dB, thats why your graph is so weird. Check out formulas in here http://zone.ni.com/devzone/cda/tut/p/id/4278
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      1. POWhy does my FFT gives a different visualizer output than Windows Media Player?
      1. USruhalde
 

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