On the other hand, Spectrogram x-axis represents time of the entire audio duration length (or some finite time frame if performed on real-time signal), y-axis represents frequency (again, linear or logarithmic scale), and the chart line itself is colorized to visualize frequency component’s amplitudes in audible range (usually 20 ~ 20000 Hz). For example, conventional Spectrum Analyzer displays frequency on x-axis (linear or logarithmic scale), and amplitude on y-axis (linear, dB, relative, absolute…). The quality of sample rate conversion can be easily visualized via Spectrogram chart, which is just a fancy Spectrum Analyzer in time-domain. If you still have trouble understanding aliasing, some theory behind sampling, Nyquist frequency and spectrum charts will help!
Sorry, but it cannot be explained any simpler than this. If the sampling frequency is not carefully selected (or the original signal is not band-limited), those spectral copies will overlap with the original signal and other copies, creating an aliasing distortion effect. In the proces of digital sampling, each frequency component in the original signal is multiplied by the sampling frequency and “shifted” as a spectral copy in the frequency domain multiple times (n = ☑ * fs, ☒ * fs, ☓ * fs, etc).
What is ALIASING? Aliasing is, in simple plain words, an overlapping distortion of multiple spectral copies of frequency components.
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