Playing sound after filtration but same sound level is heard out of PC speakers

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Alex Z 2019-10-4

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https://ww2.mathworks.cn/matlabcentral/answers/483571-playing-sound-after-filtration-but-same-sound-level-is-heard-out-of-pc-speakers

关闭： MATLAB Answer Bot 2021-8-20

I'm toying with audio filtration, built a simple high pass filter to suppress low band frequencies.

The audio carries data sampled at 44.1kHz and most energy is carried out in low band of several hundreds Hz (checked through spectrogram and pwelch functions)

After applying high pass butterworth filter of N=5, comparing the spectrum of the original and filtered out signal I confirm the filtered signal spectra looks as it should after such filtration (low frequencies are suppressed substantially).

However, when comparing the results by hearing through playback using either sound() and audioplayer() functions, I hear the same sound level in both original and filtered data, albeit the filtered one has an emphasis on the higher frequnecies (as expected due to filtraiton).

But the sound volume sounds the same ot my ears out of PC speakers. Looks like somewhere on the way to teh speaker the sound is normalized automatically, kind of AGC or volume equalization.

I'd expect the filtered sound to be heard much weaker than the original due to the most energy in the original resides in the lower band that has been suppressed by the filter.. But yet again, it sounds at the same sound level..

Any clues ?

Thanks