In a previous blog I explained what mastering was and why it is necessary. The work the mastering engineer does can be divided in two parts. Premastering, the first part of the job, was covered in the previous blog and is a more artistic task. The second part, mastering, is more technical and is today’s topic.
Mastering
Mastering, consists of preparing the actual master. It is a rather technical task and includes providing the matrix for duplication, the acetate for vinyl or the glass master for CD.
If the mastered audio is at a higher bit depth than what the final product asks for, dithering will need to be applied. Put simply, dithering adds a low-level noise print to the signal to compensate for the steps that appear when reducing the bit depth (which in effect reduces the digital word length). The typical example is going from a 24bit master to the 16bit necessary for CDs. These steps or square looking waves actually cause distortion in the audio and dithering is supposed to hide it. Different dithering algorithms exist. POW-r, which stands for Psychoacoustically Optimized Word-length Reduction, is a proprietary algorithm developed by a group of companies (including Weiss Engineering and Millenia Media) and is available in ProTools, Digital Domain, Logic, SADIE, Samplitude and Sonic Solutions.
When preparing a CD, the mastering engineer needs to add the P and Q subcodes (which are part of the Red Book specification). To put it simply, the P and Q subcode data that is integrated (multiplexed) with the audio data on the CD contains timing information (start of track, end of track, how much time is left on the CD or in the song etc…) used by the CD player. The P code tells the CD player where the start of each track is. The Q code includes the TOC (Table Of Content, written on a CD-R during the finalizing stage) and length of each track. Other subcodes exist (R, S, T, U, V and W) but only P and Q are required for an audio CD. The other rarely used codes can contain text and lyrics information for example.
Also, an ISRC (International Standard Recording Code) can be added to each track of the album. The code, unique for each track, identifies the producer, the country off origin, the year it was produced and the track itself. This code was used a lot when radio stations actually played CDs as it allowed tracking what music was aired easily.
CD Text can also be added to every track of the final master. CD Text allows information about the album to be displayed on compatible CD players, like those found in car sound systems. If you create a DDP file, it includes the CD Text information.
Questions or comments ? k.blondy@musitechnic.net
