What is "groove wear"?

To everyone who has not read this, parts of it are very useful to know:

Kevin Gray on disc mastering in the digital era:


THE following was written to aid engineers and producers who wish to release vinyl records. It is especially important for those who may be well versed in recording, but have not released vinyl records before. The paper is mainly about "pop" music , but the principles apply to all others. It was written to explain a complicated transformation in as simple terms as possible. To some it may seem very technical, to technical types it will seem simplistic. It was written for the "middle ground".



PRODUCING GREAT SOUNDING PHONOGRAPH RECORDS
(or Why Records Don’t Always Sound Like the Master Tape)

BY: KEVIN GRAY 5/3/97

The phonograph record is a marvelous medium for storing and reproducing sound. With frequency response from 7 Hz to 25kHz and over 75 dB dynamic range possible, it is capable of startling realism. Its ability to convey a sense of space, that is width and depth of sound stage, with a degree of openness and airiness, is unrivaled by anything but the most esoteric digital systems.

That having been said, it is important to understand the limitations of this medium in order to make great sounding records. The first limitation is recording time and level (volume). The amount of time possible on a record side is entirely dependent on the cutting level (volume) and the amount of low frequency information (bass). Bass uses more space than treble.

The record groove is an analog of a sound wave. Try to picture looking down on a narrow river or stream. The left bank is the left channel and the right bank is the right channel. Your turntable’s stylus is a wide round raft that is going to travel that river. For simplicity, imagine that the banks stay parallel, (left and right the same) which means the sound is monaural. The louder the sound and or the heavier the bass, the wider the whole river (and your boat) wiggles side to side. The higher the pitch (frequency), the closer together the wiggles get. In other words the sharper the twists and turns, the higher the pitch. Obviously, everything from bass to treble is happening at once, so the gently sweeping wide curves (bass guitar and bass drum) have smaller, more jagged wiggles (vocals, guitars, keyboards, cymbals, percussion etc.), superimposed on them. It should be mentioned here that if the bass information is too loud, your raft gets thrown over the embankment (skips). So now you should be able to see that the louder the music is cut, the wider the groove wiggles, and the less time can fit on the side. Or looking at it the other way around, the longer the side, the less room for wiggles (volume and bass).

Next limitation: treble. You can put as much treble on a DAT or CD as you want. Unfortunately this is not true on a record (or analog tape for that matter). Although 25kHz response is possible, excessive transients are a problem. There are several reasons for this. It was decided with the advent of the first electrical transcription phonograph record, to reduce bass and boost treble in the cutting of the master record. This reduces bass wiggles and makes treble louder. And we aren’t talking about a little bit of cut and boost here, we’re talking about a 40 dB change from bottom to top! Without the bass cut, you’d only have about 5 minutes on your LP side. Without the treble boost, you would hear mostly surface noise. You don’t have to worry about this drastic cut and boost sounding funny, because the phono preamplifier in your amplifier or receiver has an inverse curve which boosts the bass and reduces the treble by the same amounts used in cutting, so the whole process comes out linear. This was standardized worldwide in 1953 and is called the RIAA record and reproduce curves.

I said you don’t have to worry about the RIAA curve, but the cutting engineer sure does! Power amplifiers (100 to 400 plus watts) are used to drive the tiny coils (one for each channel) in the cutting head. They’re like miniature speakers which instead of just moving air, push the stylus that etches the groove in your record. With 20 dB of treble boost, you can only imagine the beating that the cutting head takes from cymbal crashes and the like. The coils are helium cooled but still can reach 200 degrees Centigrade. A circuit breaker is used to prevent catastrophic destruction. This doesn’t all add up to the limitation it seems, because it is still possible to cut levels higher than can be played back.

Let’s take a look at cymbals and vocal sibilance (those loud ‘S’ sounds). "Why", do you ask, "Do they sound OK on the tape but sometimes so awful on the record?" The answer is twofold. First, the problem is aggravated by the high frequency boost we just discussed. Further excessive boost in your mix makes it that much worse. Unlike a cymbal crash in which the impulse is short (the actual hit of the stick on the cymbal), the duration of an ‘S’ is considerably longer, so it is even more pronounced. And second, the worst part: Remember the river? Suppose the river’s twists and turns are actually tighter than your raft? Ever watch a raft attempting rapids? Well, that is exactly what your stylus is doing when it hits a loud cymbal crash or a loud ‘S’ in the record groove. At the instant that the curvature of the groove is tighter than the tip radius of your stylus (raft), it goes over instead of through ‘the rapids’, and you have 100 percent distortion. The higher the frequency and or level, the greater the curvature and distortion.

The cutting engineer can usually tell if treble peaks are going to ‘break up’ on playback, by the amount of current drawn by the cutting amplifier. This is measured by current meters on the amplifiers. If the current is excessive, the only way to prevent this is to use a very fast-attack treble limiter to reduce the intensity, and therefore, the groove curvature.

While we’re on the curvature subject, it is necessary to explain one more thing. Ever wonder why outside diameter cuts on a record sound clearer and cleaner than inside ones? Unfortunately it’s a fact. Why? The answer is geometry, curvature again. One turntable revolution at 33 1/3 rpm on an LP takes 1.8 seconds. That 1.8 seconds is spread over a circumference of 36 inches on the outside of the record. At the minimum allowable inside diameter that same 1.8 second revolution would only cover 14.9 inches. You can see from this, that a gentle wiggle spread over 36 inches would get quite ‘scrunched’ over 14.9 inches. A jagged groove at 36 inches would get really scrunched at 14.9 inches (remember the rapids). Excessive treble can even cause the cutting stylus to accelerate so fast that its back edge wipes out what the front edge just cut! It’s unfortunate, but treble rolls off, and distortion goes up as you approach the center of the record. It is quite gradual, but if you compare the source recording to the disc, this actually starts to become noticeable after the second cut or so. Any attempt to compensate for this by boosting the treble, only makes the problem worse (greater curvature remember).

I’ll discuss stereo very briefly. If the sides of the river don’t stay parallel, it’s stereo. In other words, any difference between the two channels causes the stylus to move up and down in addition to sideways. As the stylus digs deeper, it is using more precious disc space. The moral for engineers is: If you are looking for hot levels or long sides, don’t pan instruments like drums and percussion hard left and right. Keep the bass and bass drum in the center, and keep everything in phase. An out of phase snare or bass drum can wreak havoc. Use an oscilloscope if possible!

All else being equal (bass, volume and depth of cut), by allowing the end of the record to finish farther out from the label, instead of spreading the grooves farther apart to fill all the space, will actually make the record sound better. However, I understand the concept of making the record look ‘full’.

So much for the primer on record cutting. Now let me give you some additional tips on making your record sound great. First, keep it as short as possible. I know this isn’t always possible, but particularly if hot levels are important, keep it short! How short? As a general rule an LP should be under 20 minutes and 24 minutes maximum. 16 to 18 minutes is ideal. Also, try to balance the side times, preferably within one minute. If one side has to be longer, put more of the quiet material on that side. This will insure even levels. If the sides are long, remember that the more bass, the lower the cutting level (volume). It is possible to squeeze 30 minutes on a side but the level will be so low you’ll have to crank it just to hear it, and you will hear the surface noise!

A hot club record should be under 12 minutes, 8 to 10 minutes is ideal. Some of the top club DJs tell me they won’t even play records that are over 12 minutes long because they know the levels will be low and don’t want to adjust gain.

Watch excessive treble boost in the 8 to 16 kHz range in mixing, you won’t get it back on your record. You can’t break the laws of physics, sorry. A good idea is to check your mix against a record you like with lots of cymbals. If you hear a lot more sizzle on your tape, chances are it won’t make it to the record. Particularly watch those ‘S’s. Use a de’esser on vocals. I don’t do endorsements, but dbx makes a great one. This will give you more overall treble because in cutting your record, the treble limiter won’t be chomping on your cymbals too.

Put your hottest, brightest most dynamic mixes on the beginning of the disc and they’ll stay that way. If possible keep the quieter material on the inside tracks.

A word about comparing DATs and CDs to a record; digital levels do not bear any relationship to analog levels. We’re talking apples and oranges here. The analog output level of a CD player or DAT deck can be anything the manufacturer wants it to be, but it is generally higher than a phono preamp output. There are two reasons for this. First the digital equipment manufacturers want CDs and DATs to sound better (translate Louder) than records. If the DAT or CD is fairly wide dynamic range, a record can be as loud. HOWEVER, there has been a trend in the last few years to compress digital tapes almost to the point of the level display not moving from the beginning to the end of the song (second reason). This started with rap, filtered through to dance and club mixes, and finally to most new commercial pop releases. The result is that what used to be the peak level is now the average level and we’re talking 6 to 8 dB louder than is physically possible to put on a phonograph record (or analog tape). Remember that the groove can only move so far before the playback stylus mistracks or skips, and magnetic tape can only be driven so hard before it saturates. At any level, a digital recorder is only printing ones and zeroes. There is no digital counterpart. The bottom line is that a really compressed CD or DAT is going to be 6 to 8 dB louder than your record. This is not a defect, it’s a FACT OF LIFE. I prefer to think of the digital compression as a defect and a scourge to anyone who appreciates dynamic range, but now I’m editorializing.

If the levels are not matched in one of these comparisons, the compressed digital source (6 to 8 dB louder) will sound like it’s got more of everything. I’ve heard the record described as sounding like it’s under water. If the levels are matched, suddenly they sound almost identical. If you are trying to accurately compare a record with a digital source, use a mixer or preamp to raise the level of the record or lower the level of the DAT until they sound very similar and then compare.

While I’m getting things off my chest, how about making the cutting engineer’s job easier. Analog tapes are easily timed when rewinding, and have visual clues such as leaders and splices. DATs and CDRs do not. When supplying DAT tapes or CDRs for record mastering, always provide three things, please! One: Start IDs for each song, not just each side, sometimes it’s hard to tell where one song ends and another starts. Also, they’re handy for checking each song. Two: Note accurate timings for each song AND total side time including pauses. This is particularly important if your DAT deck doesn’t print absolute time on the tape. So much time is wasted by the cutting engineer having to figure out times and it’s imperative to know before cutting. Three: Any level or EQ (tonal) changes you want made. One thing to be aware of is that just because all the songs peak at zero doesn’t mean they will all be at the same apparent volume. This is also true with analog tapes, but to a much lesser degree (remember the digital level tutorial). This is where good old VU meters (with 6 dB pads) come in handy when you are assembling your DAT or CDR.

I hope you find these tips and suggestions helpful, and apply them. You may have guessed from this, that records were not originally intended to store the kind of energy today’s music contains. It’s true, but if you mix with the limitations in mind, it will make a huge difference in the final product. It’s unfortunate, but the approximately 10 year lull in the production of phonograph records, from the mid 80s to mid 90s, caused a lot of engineers to forget these limitations. In the meantime, a whole new generation of engineers has come along who never dealt with record production before. This is for you! Make some great sounding vinyl!

 

The deal is, most of the recorded "music of our life" goes up to about 15-16k on a good day. Higher than that, bias noise and other stuff we actually DON'T want to have reproduced.

Ya dig?

 

nin,

I never filter ANYTHING or do any kind of EQ stuff to get rid of top end extension or anything like that. We just run everything full bandwidth. The cutter head rolls off where it does automatically; when the limits have been reached, well out of audible hearing range. The cutter amps would blow up if they didn't....