The Oxford DeNoiser from Sonnox is a plug-in that removes wide-band noise from audio material using techniques based around the concept of a "noise profile". The noise profile is used to gate-out components of the frequency spectrum that are below it, while keeping the components that are above it.
The plug-in uses several methods to arrive at an appropriate noise floor. Auto, freeze and manual. It also contains a dedicated DeHisser section before the broadband noise-removal section. This can be used on audio such as dialogue where there isn't a lot of high frequency content that needs preserving, and where the priority is to reduce the hiss to an acceptable level.
A Mid/Side mode allows for de-noising only the Side channel, resulting in mono operation beings entirely unaffected while stereo operation produces a cleaner stereo image without affecting the center. This is particularly useful in broadcast where switching between stereo and mono should not cause a noticeable change in dominant noise content.
Often de-noising can make the material sound a little flat compared with the original. The Oxford DeNoiser has a "Warmth" control in the output section that can quickly add some richness back into the program material.
- Auto Mode
- The frequency spectrum of the signal is examined automatically to acquire the general shape of the noise threshold profile by looking for consistently present levels in the frequency spectrum
- The threshold is relative to the general signal level and therefore noise removal will always be a fixed number of dBs below the actual signal
- Freeze Mode
- Method to arrive at a noise profile by freezing the automatic noise profile and using that fixed profile going forward
- Useful for capturing the profile from a section of material containing only background noise and then applying it to the rest of the material
- The threshold is always set to remove the correct level of noise from the material, so as the level of the program material climbs the noise removal is less destructive
- Manual Mode
- User manually specifies a simple "Colored" noise profile, using the Color and Air controls
- Color adjusts the shape of the noise-profile from white to red noise
- Air modifies the high frequency shape of the noise-profile
- Additional Controls
- Ability to adjust the threshold of the noise-profile at different frequencies by means of a bias curve
- Additional bias curve to adjust the amount of reduction at various frequencies allowing more noise removal at some frequencies while still being gentle at other frequencies
- Both bias curves work in all three modes
- Further manipulation of the detect threshold and reduction amount is available in the form of the Smooth and Tune controls
- Option available to listen to the "Diff" signal (difference between the input and the processed output), useful to ensure that "good" audio is not removed from the output signal
- DeHisser section before the broadband noise-removal section
- Can be used quite aggressively on audio such as dialogue where there is not a lot of high frequency content that needs preserving, and where the priority is to reduce the hiss to an acceptably clean level
- Mid/Side Mode
- Mid/Side operation mode causes the plug-in to de-noise only the Side signal content of the Left-Right signal, leaving the Mid content alone
- The Left-Right signal is first converted to Mid-Side, the Side de-noised and then the signal is converted back to Left-Right
- Particularly useful in broadcast where switching between stereo and mono should not cause a noticeable change in dominant noise content
- In some circumstances, having removed the noise it is desirable to add something back to the signal that has been taken away
- For example, the act of de-noising can make the material sound a little flat compared with the original
- "Warmth" control in the output section can quickly add some richness back into the material