If you want a high volume and/or strong deep grooves to scratch, do not put more than 12 minutes each side at 33rpm on a 12"disc.
Compressions or treble limitations will be inevitably made if you use psichoacoustic treble enhancers, treble normalizer plug-ins, extreme treble levels... this all, aven if we cut as is, will not be played back by your playback head if not DISTORTED and DIRTY! Make a good check of the overall MIXDOWN and its equalization.

Extreme volume=short time
Extreme bass=short time and maybe jumps problems
Extreme trebles=low volume and distorted sound
Extreme stereo bass=low volume and jumps

Modified lathe
Internal head

Bass in mono, Stereo where necessary, no high frequency constant sweeps, Cut under 40Hz and over 14/15000 Hz if you want a very loud cut. The best recordings at normal level (+3Db@5cm/sec) will be better than 20 to 18000 Hz flat on the disc with harmonics extended to 25000Hz.
Stronger and loudest tracks must be put at the beginning; at the end the sound will be more close in trebles than the beginning, especially at 33 RPM. Best quality, but less surface time, at 45RPM.
Any FIXED high frequency loud tones on your tracks can not be cut because they are very dangerous for the cutting equipment and it is not possible to play them correctly by your stylus; so don’t give us tracks with fixed ultrasonic frequencies or sweeping extreme tones!!! Inevitably, they will not play back correctly: this is a physical limit of the system.
Pay attention to the out-of–phase bass. Bass MUST be IN-PHASE and if possible in MONO: If much stereo bass, or out of phase, your needle will jump out of the groove because the undesired vertical motion so, the cut will be not possible, or possible only at low volume.
Some vocal and treble types may be changed in tone and distortion type: this occurs because the radial tip of the play needle is physically different from the cutting needle, so playback tracking is not the same: speed, levels, equalizations and the type of cartridges you’ll use to play will inevitably change something in thefinal sound, but if all is aligned the sound will be very warm and with a big sense of presence, superior to the ears compared to the same original digital master!!!
We'll try not to compress anything, but sometimes this will be necessary.. pay extreme attention to your final mix: no excessive trebles, no superdeep bass stereo or out of phase, no fix treble tones... listen with your ears, don’t just look at the spectrum! If you are working with a 24bit soundcard, the best way to get back the best on vinyl is to give us a 1/2" REEL analog tape recorded at maximum speed of 38cm/sec... the tape and the analog way will be the best media for the vinyl mastering with an exceptional sound quality.
If you send us a tape reel, please record three reference tones of 100/1000/10000 Hz at 0 Db at the head of the tape; this is necessary to align the azimuth of our playback tape head to your recorder and calibrate the NAB tape equalizer to obtain the best performance possible before the "tape-to-disk" transfer(historical process).
If your master comes out perfect with this some simple piece of advice (not necessary in digital recordings) you will like your vinyl much more than your own master..
We try to cut at the maximum level possible depending on the material you send us and how longer it is: best time per side for the maximum level possible is about 13min at 33rpm and 10min at 45rpm on a 12"; on a 10" the time for the maximum level is about 8min at 33rpm and 6min at 45rpm ( +6 to +8Db US Standard or +12Db peak referred to the standard recording level of 5cm/sec).
All cuttings will be made with the industry standard Neumann cutterheads ourself customized and primarily with tube amplifiers because we like vacuum tube sound!!.
After you have prepared the media (AUDIO CD-R/DAT/MD/TAPE REEL/CASSETTE/MP3)for the vinyl transfer, specify clearly on paper all the instructions for us, such as: 16/33/45 or 78 rpm speed, particular blank spaces on the disc, which tracks are to cut, better yet if all tracks are in order with 3 to 5 seconds of blank space between one another.
Put your stronger tracks with more trebles and more volume at the beginning of the disc... the last grooves will sound closer and lower in volume than the first. At the end of a 33rpm disc, some distortion may occur, especially on strings and vocal sibilants... some kinds of vocals may change in certain tonalities.
Send all in a secure envelope with postal tracking number to be sure it doesn’t get lost. Keep a copy of your master work for safety.
Write your address, phone number and/or e-mail precisely and clearly, in order to send back your "freshly cut" discs.