Found this a rather interesting article:
http://www.emusician.com/tutorials/learn_mixing_vinyl/Learn Mixing | Tips for Mixing for VinylMay 1, 2011 9:00 AM, By Gino Robair
Vinyl records are very much in vogue again, as much for their sonic quality as for their collectability. To get the best sounding results when pressing a record, you need to consider the physical limitations of the medium before you mix. Here are some tips for maximizing the sound of your record, the first time around. when pressing vinyl, you�ll trade off program length versus audio quality, so begin by determining how much music you want on each side of your record. An LP typically holds less than 30 minutes of music, and the width and spacing of the grooves plays an important role in the sound quality of a vinyl record.
Keep in mind that the volume level at which you can cut the tracks is proportional to program length. If you want the record to be loud, you need the largest grooves possible. However, wide grooves take up physical space, so you�ll need to keep the timing of each side short if you want maximum volume.
Speed also plays an important role. Like analog tape, the faster the vinyl media moves, the better the sound reproduction will be, but the more media you�ll need. For example, the hottest playback signal will come from a 12-inch pressing at 45 rpm, which is one reason why it�s the preferred format for dance music. However, the optimum program length of a disc at that size and speed is around 9 minutes per side�great for an extended remix, but not much for a full album. Even with a maximum length per side of 15 minutes at 45 rpm, it may not offer enough time for your project. At 33 1/3 rpm, a 12-inch yields a maximum length of about 22 minutes per side, although the optimum length is around 14 minutes.
To make a record longer, you will have to cut it at a softer level to fit more grooves into the same amount of space. The softer level also means you�ll have an increase in the noise floor.
FREAKY FREQUENCIES
Low frequencies also require a lot of space on a record. If your music is bass-heavy, you�ll want to have fewer songs on the release, to leave room for wider grooves.
Keep an eye on the level of your low-end: Excessive bass will cause a needle to skip, and mastering engineers will tame this frequency range if they think it�ll cause a problem during playback. In addition, low frequencies are panned to the center during the mastering process, and the crossover frequency differs between mastering houses. It�s recommended that you mix the bass instruments to mono, so that you have control over the sound before it gets to the mastering studio.
Excessive high frequencies can also present a problem on vinyl, particularly sibilant vocals or sharp transients which will distort during playback. Mastering engineers recommend using a de-esser on vocal parts. In addition, too much compression and limiting in the final mix will exaggerate the highs, making it difficult to cut a good vinyl master.
It�s also important to understand that the quality of high-frequency reproduction diminishes as the needle gets closer to the center of the disc. If you boost the highs to compensate for this, you�ll end up with a record that distorts. One popular approach is to sequence the songs so that the loudest tracks are at the beginning of the record, where the stylus has the greatest distance to travel, allowing it to accurately reproduce the upper registers.
ANALOG OR DIGITAL MASTER?
Consider the media that you use to deliver your mixes to mastering. If you�re pressing to vinyl because you prefer the sound quality of analog sound over digital, you�ll want to mix to something other than CD. Many artists deliver their mixes on analog tape, from which the mastering engineer will cut the master lacquer. Select the mastering lab before you mix, and find out which tape format it prefers.
An alternative is to mix to a high-resolution digital format and deliver the files on a DVD-R or upload them to the mastering lab�s FTP site. Each of the 16 songs of Arcade Fire�s recent Grammy winning release, The Suburbs, was mastered to vinyl from 24-bit, 96kHz mixes, and then re-digitized from the lacquer masters at 16-bit, 44.1kHz for release on CD and MP3. This allowed mixer Craig Silvey and mastering engineer George Merino to impart the characteristic timbre of vinyl to the subsequent digital release.
But no matter how you deliver the mixes, be sure to document the song order and timings, as well as the length of time you want between songs. If your master is on tape or CD, add a few minutes of silence between the last song of side one and the first song of side two, so that it�s clear where one ends and the other begins.
In all cases, find out what the mastering house wants to receive before you mix. That way, you don�t waste money and time redoing one of the steps in the process.
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