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| WaveWarp 2.0 Example DrawingBoard
SpectrumAnalyserWithDownSamplingEducationalExample
Description
Spectrum Analyser with DownSampling Educational Example
Illustrates the use of the Spectrum Analyser block in combination with down-samplers to explore very low frequency
regimes. The Sine Wave Generator is set to produce a pure tone of 10 Hz (inaudible !) which is extremely low compared to
the default sample-rate of 44100 Hz. The upper Spectrum Anlayser running at default sample-rate of 44100 Hz attempts to
analyse this signal directly. With the default settings (window length 8192 samples, FFT length 8192) the corresponding
frequency resolution is about 5 Hz (i.e. 44100 divided by 8192), which, as you can observe in the display, is barely
sufficient for analysing this low-frequency signal. This is a basic limitation of the FFT, namely that the frequency resolution is
limited by the sample rate and data buffer length.
To circumvent this limitation, the lower Spectrum Analyser is configured to run at a sample rate which is 125 times lower i.e.
352.8 Hz. This is achieved by down-sampling the original signal in three successive stages (down by 5 each time,
incorporating an anti-alisaing filter at each stage). Now the frequency resolution is improved by a factor of 125. For the
same data buffer length of 8192 samples, the resulting frequency resolution is about 0.04 Hz (i.e. 352.8 divided by 8192)
which, as you can observe in the display, is perfectly capable of analysing the 10 Hz signal !
NOTE: you must wait for the total "latency" of at least 23 seconds (i.e. 125*8192/44100, plus a screen refresh cycle of 11
seconds) before the display reveals anything -- but when it does, the very high frequency resolution will be readily apparent
!
This extreme example nicely illustrates the versatility of WaveWarp's multi-rate engine !
Components used:
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