将正弦波中的时间和频率转储到 csv 中

Question

Am just plotting a sine wave and doing a plot spectrum analysis(similar to the one which is in audacity).

To plot i have a function like:

pxx, f, t, ax = plt.specgram(
    audio_data, NFFT=size, Fs=rate, noverlap=0, cmap=plt.cm.binary,
    sides='onesided', window=signal.hann(size), mode='magnitude')
plt.plot(f, 20 * np.log10(np.mean(pxx, axis=1)), 'b')

This function plots as expected. But i need to dump the frequency and time of the sine wave into the file in the below format.

Time(secs)    Freq
0.5           100
1             200

Is there a way to do this using the values returned in specgram.

Please note am pretty new to audio analysis am just learning my trade. Any help would be appreciated.

Answer 1

The Matplotlib specgram helper automatically segments your signal and runs FFT on it, so you end up with an image. That won't help you much for outputting text data.

In addition, at any given point in time multiple frequencies will exist in the signal (yes, even a monophonic sine wave due to FFT imprecision), so you can't describe a signal at any given time with just a single "Freq" value. You could, however, figure out a peak frequency for a time window.

You can find the source for specgram here if you feel like adapting it, but it might be better to look at SciPy's FFT functions (or this tutorial ) so you get numeric data from the get-go.