Ask the Engineer with Scott Hull: How Much Music Fits on an LP Side?


Ask the Engineer is a series on the Masterdisk blog where our engineers answer questions about music production.

SCOTT HULL is a 28-year veteran mastering engineer and the owner of Masterdisk studios in NYC. Scott started his career in 1983 and has mastered hit records and classic albums in every genre, as well as many Grammy-winning titles. He is widely regarded as an expert in vinyl mastering. Recent projects include albums for Donald Fagen, Sting, Dave Matthews, Glenn Frey and KISS, as well as multiple albums for the Sh-K-Boom, Tzadik and Luaka Bop labels. Over the course of his career Scott has mastered albums for Bob Dylan, Bruce Springsteen, Miles Davis, Lou Reed, Ravi Shankar, Herbie Hancock, Tom Zé, John Mayer Joe Bonamassa, and many more.

Photo of the Masterdisk latheQ: How many minutes of music will fit on the side of an LP vinyl disk?

A: It’s a simple question with a complex answer. Many websites publish charts explaining how much music fits on one side of a vinyl record. The main purpose of those guidelines is to make it easy for the cutting engineer to do his job. But do you want to have an average record or an extraordinary one? Ah, I thought so. You need to read on.

Lets just say, for argument’s sake, that we wanted to cut a vinyl side with a 1k test tone (midrange near a middle B on the piano). Pretty boring “music,” but this control measure will help me explain the process. And lets say that that tone an be cut on a particular lathe at a level of 0db and at a duration of 30 minutes. The relationship between level and duration is due to the fact that a louder signal cut into the disk takes up more room on the disk and thus the grooves have to be farther apart to avoid cutting over themselves.

Now lets take the tone generator and lower the frequency to 500hz (down one octave). Cutting this signal at the same level as the 1k tone, we will run out of disk near 24 minutes. The bass frequencies have longer wavelengths and use more space as they squiggle back and forth.

Lower it another octave to 250hz and we run out of disk at 18 minutes. Surprised? So how can we possibly cut rock and roll, with energy down to 20hz, for more than 20 minutes? There’s more to the story.

Let’s go back to 1k. Remember, it fit on the LP side for 30 minutes. If I lower the level 1 db, we can now record 33 minutes of tone on the disk. Wow, only 1 db? The reason is that it’s 1 db throughout the entire side: the average level is down all the way across the disk. This is very important.

Then let’s raise the level to +2 db from the first test. What do you expect to happen? We run out of disk at 25 minutes. That’s 5 minutes less audio recording space with just a 2 db raise in level. So level is king, bass is queen and hi-frequencies are the jack, ten and nine. Remember we are still talking about simple test tones, not music.

The point I’m trying to make is that music doesn’t obey rules of thumb. No two projects are the same. Even if the music was identical, two different producers might have different objectives. One might want the record loud, another may be more concerned with being very high quality / low distortion and might not mind a slightly lower level.

Before you decide if your music “fits” on a side please talk to your cutting engineer. The engineer has to listen to your music, and measure how his or her lathe will respond to your music. Anything will fit if you turn the level down far enough. Don’t just send your cd master to the vinly pressing plant asking for an “average” cut. Your music doesn’t have to sound average on vinyl – it should sound amazing! And you already know who to contact to make that happen. (That’s me!)

I’ll go a little deeper into the grooves next time when I talk about what happens when we aren’t cutting mono test tones. I’ll give you a hint… the grooves get deeper and that causes them to take up more room on the disk. Uh oh…

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