Apple Logic Express 7 - Manual (Page 69)

Chapter 10 Special 69
If the noise floor of your recording is very high (on recordings from cassette—more
than
−
68 dB), you should be content with reductions of 83 to 78 dB, provided that
there aren’t any plainly audible side effects. After all, you have reduced the noise by
more than 10 dB, which is less than half of the original volume.
Noise Type
This value effectively states what type of noise you think the material contains:
• A value of 0 means white noise (equal frequency distribution);
• Positive values change the noise type to pink noise (harmonic noise; greater bass
response),
• Negative values change the noise type to blue noise (Hiss—tape noise).
Smoothing
The Denoiser uses FFT (Fast Fourier Transform) analysis to recognize frequency bands of
a lower volume and less complex harmonic structure, and then reduces them to the
desired dB value. In principle, this method is never exact, as neighboring frequencies
will also be affected.
If you use the Denoiser too aggressively, the algorithm will produce artefacts, such as
“glass noise” which—in most cases—are less desirable than the existing noise.
Therefore, there are three parameters for reducing this effect in all three dimensions of
sound:
• Time Smoothing
This is the simplest form of smoothing. This parameter sets the time required by the
Denoiser to reach (or release) maximum reduction.
• Frequency Smoothing
This parameter sets a factor for smoother transition of the denoising to neighboring
frequencies. More precisely: If the Denoiser recognizes that only noise is present in a
certain frequency band, the higher the Frequency Smoothing parameter is set, the
more it will also change the neighboring frequency bands to avoid “glass noise”.
• Transition Smoothing
This parameter sets a factor for smoother transition of the denoising to neighboring
volume levels. More precisely, if the Denoiser recognizes that only noise is present in
a certain volume range, the higher the Transition Smoothing parameter is set, the
more it will also change similar level values to avoid “glass noise”.
The Graphic Display
The graphic displays how the lowest volume levels of your audio material (which
ideally is only noise) will be reduced.