The term mastering is often misunderstood by those arriving in the world of audio technologies, especially for a short time. Mastering is the fundamental process that links the mixing phase and the CD printing phase by special industries. Its main purpose is to transform a series of pieces by an artist or different artists (in the case of a compilation) into a single and cohesive project through different technical-artistic passages.
Surely this task cannot be relegated to preset of a plugin, nor can one think of entrusting a poor project to a mastering engineer hoping I can get back a song from Hit Parade as one might mistakenly imagine. So, wanting to mention the law of conservation of the mass of Antoine Lavoisier “Nothing is created, nothing is destroyed, everything is transformed”, in mastering quality is not created, it is not destroyed (in theory) but is transformed (for better or for worse). A music program that presents unsolvable problems upstream will not return a better product after mastering, indeed most of the time the result could be even more disastrous with a clear accentuation of the defects that it was intended to eliminate. Here are some basic steps of the burning process:
- Convert all songs to be burned in the same format.
Starting a mastering session correctly, importing and converting all the songs in the same format, is a fundamental step for the success of the whole process.
- Choose the order of the songs.
The choice of the order of the tracks of an album is a key point, as it helps to keep the listener's attention throughout the duration of the record. Depending on the type of production, these decisions can be made by mutual agreement between the producer, the artist and the mastering engineer.
- Create fades and pauses between songs.
Setting fades and pauses between songs can be directly linked to choosing the order of songs.
- Fix possible stereophonic image defects, glitches or noises etc.
In this phase, mainly of a technical nature, we try to correct any imperfections.
- Bringing tracks to uniform volume levels that are competitive for the market.
With the use of different dynamics and signal processors, the RMS level of the music program is increased, trying to create a certain uniformity between the different tracks.
- Check and correct the frequency response based on the media that will play the song: cd, radio, TV, iTunes, vinyl etc.
Among the various purposes of mastering is to make listening usable in the various situations listed above; however, in some cases, it is necessary to create several versions of a piece in order to adapt it in terms of sound performance to the media or system that will reproduce it, using filters and equalizers and also referring to the passband of the media for playback.
- Add codes PQ e ISRC.
I PQ codes e ISRC they are collected in a spreadsheet that printing companies use for duplication. The PQ codes contain information regarding the length of the songs, the beginning and end of each track, pauses etc.
The musical program, therefore, passes through a series of processors that make up the so-called mastering chain.
An example of a mastering chain could be composto:
- Equalizer
- Stereophonic image processor
- Dynamic processors
- Post-Equalizer
- reverberation
- Limiter
- Dither
Some elements of this chain are interchangeable or unnecessary. Let's start with the first element of the chain:
The equalizer.
The equalizer, located at the beginning of a mastering effects chain, usually has the purpose of defining the sound: it performs the same task as a sculptor who derives a shape from the rough stone, materializes an idea; therefore we will work purely in attenuation, intervening on frequencies that are too present or on annoying resonances and proceeding gradually in the cutting phase (just think that 1db of attenuation is rarely exceeded, but in any case there are no pre-established rules as each case is separate ). Another usual intervention is to use a high pass filter to eliminate the subsonic frequencies that undermine the circuits of peak detection dynamic processors (especially analog) triggering them even when not necessary. The cutoff frequency may vary from 20Hz if you want to be more conservative, ai 30-40Hz if you want to be more drastic. As the cutoff frequency increases, the slope of the filter must also increase so that, once in the audible band (above in 20HZ), no traces of fundamental frequencies remain in that range, thus exploiting the ability of our brain to reconstruct them psychoacoustically through the presence of harmonics.
Another reason to use a high pass filter is to eliminate the DC offset due to a problem with non-linearity of the A / DD / A converter in the registration or export phase or even at a poor level of design of the power supply stage preamps. This results in a shift in the level of electrical 0 compared to digital 0 which can lead to a perceptible degradation of the audio quality or even worse to a fatigue of our acoustic apparatus due to a continuous voltage in the speakers for the entire duration of the song. With some mastering software it is possible to check for the presence of DC offset and to eliminate it automatically by using a voltage compensation system even if, the best system is the use of a high pass filter with a cut-off frequency even at 1Hz. or in any case generally below 10 Hz.
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