Processing Shellac Records
Shellac records (eg 78's) are more difficult to process than vinyl because there is a greater amount of surface noise. This type of noise is particularly difficult to remove because it is too continuous for the click to detector to be fully effective but too spiky for the hiss filter to be fully effective
The best technique is therefore to run the click filter for several passes to remove most of the impulsive noise and then to run the hiss filter at its gentlest 8dB setting to mop up some of the remaining noise.
Large diameter shellac records will have a noise profile that varies as the record plays. This is because the stylus velocity increases as it travels towards the centre of the record. This causes the noise spectrum to skew linearly with time. To accommodate this effect, Wave Corrector allows you to specify two noise profiles, one at the start of the record and another at the end. The program calculates a moving average of these two profiles to provide an optimum match of the surface noise. Use the Waveform - Edit Noise Profile command to set a dual profile.
When recording shellac records, if possible run your turntable at a lower speed (eg 45rpm) and use Wave Corrector's speed conversion feature to compensate for this. This allows you to make a recording with a lower stylus velocity and hence lower distortion.