Sonnox Oxford Restore - Manual (Page 26)

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well below valid signal components, but well above the noise floor. If Thresh is set too high,
some of the signal will be attenuated; if it is set too low, the noise removal will be less effective.
The Oxford DeNoiser provides different means to arrive at an appropriate noise profile. The
default method is called Auto mode. In Auto mode the frequency spectrum of the signal is
examined to automatically acquire the general shape of the noise profile by looking for levels in
the frequency spectrum that are consistently there. In Auto mode the threshold level is a value
relative to the general signal level. The advantage of Auto mode is that the threshold follows the
signal level so that noise removal will always be a fixed number of dBs below the level of the
actual signal. As the level of the material dips closer to the noise floor, it does not get removed
along with the noise.
Another method to arrive at an appropriate noise profile is to use the Freeze button to freeze the
automatic noise profile, and use that fixed profile from then on. This is useful for capturing the
profile from a section of material containing only background noise, and then applying it to the
rest of the material. In Freeze mode, both the noise profile and the level at which it is applied
are fixed. The advantage of Freeze mode is that the threshold is always set to remove the correct
level of noise from the material, meaning that as the level of the material climbs, the noise
removal is less destructive. However, as the level of the material dips closer to the noise floor,
more and more of the actual material gets removed along with the noise.
A third method is to use Manual Mode. In this mode you manually specify a simple coloured
noise profile. In Manual mode, both the noise profile and the level at which it is applied are
fixed.
Generally, you will want to leave the Auto mode on because in this mode the level of the
threshold will follow the general level of the signal, and this tends to give the most sympathetic
results.
5.2
Noise Threshold Bias Controls
For additional manual control over the noise threshold profile, there is a 17-step threshold bias
curve coloured red. This adjustment of the threshold profile works in all three modes – Auto,
Freeze or Manual. Using this bias curve and the drag handles, you can easily make the
threshold, and thus the noise removal, more sympathetic at critical frequencies. Lowering the
bias handles will reduce the noise reduction there and preserve more of the original audio.
Lifting the handles will increase the noise removal.