Why my spectrogram have negative values?

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Jessie Bessel
Jessie Bessel 2018-3-10
回答： Kaiwen Zhao 2020-3-14
In this figure we have a exponential sine wave and his spectrogram. My question is why the spectrogram have negative values? (from -50 to -150)

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Star Strider
Star Strider 2018-3-10
Assuming he spectrogram function plots the power spectral density (PSD) in decibels. The values are relative, not negative, amplitudes, so -150 dB corresponds to an amplitude of about 3.2E-8.

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Kaiwen Zhao
Kaiwen Zhao 2020-3-14
It's Power/frequency(dB/Hz), using log.

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