After the 1-pass and 2-pass scratch removal procedures there should remain only the signal and non-impulsive noise. Its probably fair to say that up to this point CEDAR is purely attempting to restore the signal to its original state.
The next step along the road to enhancement is Dehiss, where the operators judgement is critical to the results from the process. Fortunately, Dehiss works in real time, so given a keen ear and a good acoustic environment it should be possible to find an optimum point where all the bath water has been thrown away but the baby has been wholly left behind.
Firstly a fingerprint is taken of the noise spectrum, from a section of the recording which is without signal. Then, during processing, the software decides on a moment to moment basis whether or not noise is present, and if it is, it is removed. Note that this is not done by equalising with the inverse of the noise curve. EQ in CEDAR is a separate process. There are two main parameters which the operator must adjust correctly: the Multiplier which sets the decision level at which CEDAR will say This is probably noise so Ill get rid of it and the Attenuation which defines the residual noise level after processing. Roughly speaking, the Multiplier adjusts the effect between hissy and dry, and the Attenuation adjusts between warbly and sounds OK. The range of defects it is possible for the process to produce is some way removed from the conventional boundaries of audio malaise so description is difficult, but for any recording there should hopefully be a combination of parameters that has a solely beneficial effect.
Once Dehissed, the recording can be Equalised with CEDARs 512 band EQ (Im afraid I didnt count them). Referring back to Figure 1, an interesting feature is the ability to split the signal into 90% signal/no noise and 10% signal/100% noise components. If the portion that contains only the signal is equalised, then it is apparently possible to get 30dB to 50dB of noise free equalisation!Come on the FREE COURSE TOUR
Great home recording starts with a great home recording studio. It doesn't need to be expensive if you know how to select the right equipment for your needs.