Useful Preprocessing

In many cases, results are improved through the use of preprocessing of the spectrum prior to peak finding. Examples include the following:

• Pre-emphasis: Equalize the spectrum so as to flatten it. For example, low-order linear-prediction is often used for this purpose (the ``flattened'' spectrum is that of the prediction error). In voice coding, first-order linear prediction is typically used [162].

• Masking: Small peaks close to much larger peaks are often masked in the auditory system. Therefore, it is good practice to reject all peaks below an inaudibility threshold which is the maximum of the threshold of hearing (versus frequency) and the masking pattern generated by the largest peaks [16]. Since it is simple to extract peaks in descending magnitude order, each removed peak can be replaced by its masking pattern, which elevates the assumed inaudibility threshold.