Preparing audio for a vinyl record is not as complex as it sounds (translation from french in progress)
All the sound information is contained in only two grooves: one for side A & one for side B. Nothing more. Each frequency is represented by more or less ample movement that the playback stylus will make when the disc is on the turntable. The bass take up a lot of space, while the treble creates very fine movements up to more than 20kHz. All the frequencies are thus represented: within a bass line wich undulates slowly, the snare drum or the voices will apply smaller excursions that the playback stylus will try to follow. Not all phono cells have the same ability to follow every detail. Very high-end - and very expensive - cells will be able to do it perfectly well, while the vast majority will track the groove a little less precisely. The role of mastering - and before that of the mix - is to maximize the rendering of playback with any cell.
If the mix is intended for several supports (CD, streaming, vinyl ...), no need to do one dedicated to vinyl, it is the mastering step which will take care of making i compatible. There are still some special features to take into account, and if you integrate them into the mix, mastering will be all the more effective.
TIME IS THE KEY
This is the first to be taken into consideration. The 12, 10 or 7 "discs will determine the duration that we can reproduce. See the FAQS for playtimes, depending on the size chosen. Basically, it will be necessary to sacrifice volume and / or sound quality for longer times.
ABOUT THE BASS
If the first discs appeared in the 1950s were not very heavy in the low-end, it is almost impossible to imagine a song today without it. And that's good, because vinyl is able to reproduce very deep and powerful bass. But as these physically occupy a lot of space, if their frequency is too low (less than 40Hz), they will force the stylus to make large movements, risking to get it out of the groove, and preventing reading, by jumping, or by failing to read the other frequencies correctly, causing distortions, or "tracking" errors.
A stereo that is too wide will further increase the space required to cut them, and will decrease the time available on each side. By tightening the stereo only for these frequencies, we will be able to burn more, with better rendering. Below 300 Hz, we prefer mono, below 150 Hz, it is essential.
So that your songs are rich in bass, be sure to tighten them well, to filter almost everything that is before 40 Hz, and to pay attention to phase problems.
WHAT ABOUT THE TREBLES?
The medium and treble are very well reproduced on disc, it is in this frequency band that expresses the warmth of the vinyl, the listening comfort. The only thing to remember is that their best reproduction is at the beginning of the disc, where the speed of playback is the higher. Prefer for the last, quieter songs, a little less strong, rather than the "in your face" which will prefer the beginnings of face.
ABOUT THE PHASE
Another important feature is that of the phase. What happens when two signals are "out of phase"? The result becomes weaker, until the extreme case where the signals can cancel each other out. This results in a groove by its narrowing, even its disappearance. It is therefore impossible to cut signals out of phase. The problem is particularly important at the bottom of the spectrum, where phase shifts can drastically reduce the depth of the groove, and again pose tracking problems.
So be careful on your kick, bass, or any other instrument that tickles the bottom of the spectrum, to respect the phase alignment.
BE VIGILANT WITH SIBILANTS
The RIAA transformation which is applied in a standard way on all vinyl records & which will be "decoded" by your phono preamp during playback, sometimes over-represents the sibilants which can appear aggressive. Be sure to process your voice tracks and overheads well, the deesser must accompany you. If it is still possible to treat this problem during mastering, it is preferable to anticipate it in the mix, in order to apply surgical treatment on the only tracks that are problematic. Once the mix is made, the deesser will necessarily affect the rest of the sound content.
BE CAREFUL WITH THE DISTORTION
For the same reason as the sibilantes, the distortions will be most of the time accentuated once the sound put on vinyl. If these are not desired, be sure to check them before the mastering step. If they are part of the artistic intention, know that they can be slightly more marked.
WHICH HEADROOM FOR YOUR MIXES?
For the mastering to be effective, the peaks must be between -6 and -3 dbFS. Beyond that, the dynamic reserve is weak. The use of a limiter to lower the level of a loud mix to -3dBFS is not recommended: it does not give any additional dynamics, and does not allow effective mastering. For 7 "discs it is preferable not to exceed -4dbFS.
It is important to respect this dynamic reserve, otherwise the mastering engineer will not be able to optimize the audio content correctly. It can be counterproductive, including for the final level of your songs, to mix them louder than -3 dbFS.
ABOUT THE RMS LEVEL
This one has little importance, since it will not be the same once on vinyl. The recording time will determine the final level: the shorter it is, the louder the disc will sound. If you followed the advice below, the engineer who will be responsible for cutting your lacquer can cut it louder than if the stereo in the bass is wide, there is a lot of sibilance. When viewed under a microscope, overlapping grooves create tracking problems and jumps. To cut at a high level, you must reduce the duration of the recording (eg the Maxi 45T). There will then be enough room for the strongest modulations to be transcribed.For a 12" 45RPM maxi, the available space is the same as for an LP, for often two or three titles. This allows to soften the constraints of volumes or stereo, at the cost of less time available on the cake ( 7-9 minutes vs 19-22 minutes).