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Audio spectrum monitor
This analyzer displays an audio wave form in real-time like a digital oscilloscope and a FFT spectrum analysis.
The digitized data blocks are transformed in FFT and it is displayed as spectrum bars into left half (64 dots) of LCD. The wave forms are displayed into right half (58 dots) with edge aligning to still cyclic sygnals.
The FFT operations are done in 16-bit fixed-point. These 128 point FFT processes, applying window, butterfly operations and scalar output, could be executed in real-time (within 7.3 msec). This is pretty fast considering it is processed with only a cheap microcontroller. The spectrum bars are displayed in order of fundamental frequency x 0 (DC component), fundamental frequency x 1, x2, x3, ... from left to right. The sampling frequency is 9.6 kHz and the fundamental frequency (frequency resolution) becomes: 9.6k / 128 = 75Hz.