User Manual

16
AUDIO REPAIR
AND ENHANCEMENT
This is why having a detailed spectrogram display is so important to doing audio restoration. It helps you
clearly see the problems that you’re trying to fix.
SPECTROGRAM TYPES
Not all spectrograms are created equal. An algorithm known as the “Fast Fourier Transform,” or FFT for
short, is used to compute this visual display. Many products that feature a spectrogram display allow you to
adjust the size of the FFT, but what does this mean for audio repair and restoration? Changing the FFT size
will change the way the algorithm computes the spectrogram, causing it to look dierent. Depending on
the type of audio you’re working with and visualizing, this may help. As a rule, higher FFT sizes give you
more detail in frequencies (frequency resolution), while lower FFT sizes give you more detail in time
(timeresolution).
If you’re trying to identify a plosive, mic handling noise, or other muddy low-frequency information, a
higher FFT size in your spectrogram settings will help. If you’re trying to identify a high frequency event, or
working with a transient signal (such as a percussion or drum loop), choose a lower FFT size.
The following image is of a drum loop in a live concert setting, with a member of the audience whistling.
You can see how the dierent FFT sizes aect the way we see high vs. low frequencies, as well as tran-
sients vs. sustained notes.