| 1 | Spectrum analyser demo app
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| 2 | ==========================
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| 3 |
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| 4 | Introduction
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| 5 | ------------
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| 6 |
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| 7 | This application is a demo which uses the QtMultimedia APIs to capture and play back PCM audio. While either recording or playback is ongoing, the application performs real-time level and frequency spectrum analysis, displaying the results in its main window.
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| 8 |
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| 9 |
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| 10 | Acknowledgments
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| 11 | ---------------
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| 12 |
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| 13 | The application uses the FFTReal v2.00 library by Laurent de Soras to perform frequency analysis of the audio signal. For further information, see the project home page:
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| 14 | http://ldesoras.free.fr/prod.html
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| 15 |
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| 16 |
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| 17 | Quick start
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| 18 | -----------
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| 19 |
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| 20 | Play generated tone
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| 21 | 1. Select 'Play generated tone' from the mode menu
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| 22 | 2. Ensure that the 'Frequency sweep' box is checked
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| 23 | 3. Press 'OK'
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| 24 | 4. Press the play button
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| 25 | You should hear a rising tone, and see progressively higher frequencies indicated by the spectrograph.
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| 26 |
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| 27 | Record and playback
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| 28 | 1. Select 'Record and play back audio' from the mode menu
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| 29 | 2. Press the record button, and speak into the microphone
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| 30 | 3. Wait until the buffer is full (shown as a full blue bar in the top widget)
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| 31 | 4. Press play, and wait until playback of the buffer is complete
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| 32 |
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| 33 | Play file
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| 34 | 1. Select 'Play file' from the mode menu
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| 35 | 2. Select a WAV file
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| 36 | 3. Press the play button
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| 37 | You should hear the first few seconds of the file being played. The waveform, spectrograph and level meter should be updated as the file is played.
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| 38 |
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| 39 |
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| 40 | Things to play with
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| 41 | -------------------
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| 42 |
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| 43 | Try repeating the 'Play generated tone' sequence using different window functions. These can be selected from the settings dialog - launch it by pressing the spanner icon. The window function is applied to the audio signal before performing the frequency analysis; different windows should have a visible effect on the resulting frequency spectrum.
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| 44 |
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| 45 | Try clicking on one of the spectrograph bars while the tone is being played. The frequency range for that bar will be displayed at the top of the application window.
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| 46 |
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| 47 |
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| 48 | Troubleshooting
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| 49 | ---------------
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| 50 |
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| 51 | If either recording or playback do not work, you may need to select a different input / output audio device. This can be done in the settings dialog - launch it by pressing the spanner icon.
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| 52 |
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| 53 | If that doesn't work, there may be a problem either in the application or in Qt. Report a bug in the usual way.
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| 54 |
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| 55 |
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