Metallica’s song “Master of Puppets” has extremely powerful and driving momentum, which is especially impressive given that it is riddled with meter changes and thrashes on for almost nine minutes. The 1985 album of the same name, on which the song was released, was praised by all sorts of critics, and is commonly described as one of the best metal albums ever released. The title song in particular is a fan favorite, and is a staple of the band’s live sets. “Master of Puppets” is also one of Metallica’s most popular songs among aspiring guitarists, and the number of home-made transcriptions of this song available online is simply staggering — for example, ultimate-guitar.com has at least 45 separate tabs of this song alone, not including tabs of the whole album.

But I feel kind of funny every time I look at a transcription of “Master of Puppets.” There’s a lot of changing meter in this song, and there’s one riff in particular in the verses which has several measures of 4/4 followed by what is usually transcribed as a single measure of 5/8.

The problem is that on the album version of the track and in some live recordings, it doesn’t really feel like an even 5/8 — the rhythm is consistently off enough that if you try to tap out really strict eighth notes, you end up not being with the band when you get through to other side. There’s a lot of research literature within the fields of music theory and music cognition which focuses on such “microtiming deviations,” but most of this research deals with rubato (slowing down and speeding up in the course of a phrase) or differences in timing between a solo instrument and the accompanying ensemble. That doesn’t seem to be what is going on here.

To get a better understanding of what was happening, I opened up the album version of the song in Audacity (a free sound-editing program) and started measuring the timings of Metallica’s performance. In the spectrum viewing mode, it is very easy to see the drum articulations in most rock recordings, and with close zooming it is fairly easy to place a label on each important beat with an accuracy around 2 or 3 thousandths of a second. The status box at the bottom of the window tells you the exact timing of this label down to more decimal places than could possibly be practically useful. Subtracting the timing of one label from the next previous label calculates what music scholars call the “inter-onset interval,” in other words, the duration between the start of one note and the start of the next. This method makes it easy (although a bit time-consuming) to closely study the rhythmic feel of any recorded performance with drums or some other instrument with clear articulations, such as piano or guitar.

I wanted to be thorough, and measure enough timings of this pattern to get a good average, but I do still have a life outside of music research, so I only looked at the occurrences of this pattern in the first verse. That still gave me eight instances of the 5/8 pattern to study. I measured the surrounding quarter note beats for comparison, which are mostly clearly marked by the drum pattern. If you look at the chart below, there is a clear and surprisingly consistent pattern to how Metallica performs this rhythm.

As you can see, Metallica’s timing keeps pretty consistently to .15 seconds for an eighth note and .29 seconds for a quarter (or two eighth notes), except for the middle of the 5/8 measure. After the first three eighth notes of this measure, you can hear a brief pause before the last two eighth notes, a pause which is almost always .04 or .05 seconds (about a third of an eighth note), and which makes the measurement of these two eighth notes grouped together .34 or .35 seconds. What makes this rhythmic idiosyncracy different from what has been studied by most music theorists is that this slightly attenuated beat is performed by the whole ensemble in unison, and it’s not a delay that is “made up for” right afterwards. In other words, it’s not a local deviation from the beat that maintains the pulse over a longer span of music, but a permanent shift of where the beat occurs.

This 5/8 measure deliberately disrupts the song’s pulse as much as possible. Even if the band played the eighth notes in straight timing, the quarter note pulse and half note pulse would both be disrupted by the odd length of the 5/8 measure. The 5/8 measure places accents on the second and fourth eighth notes, against the pulse of the preceding 4/4 measures, but then the following measures continue to reinforce this new location of the beat.

For a long time, I thought that the transcriptions I’d seen were all wrong, that this riff did not have a 5/8 measure in it, but until I measured it I wasn’t sure if my ears were fooling me or not. I still think this is a valid question; 5/8 is “supposed to be” five equally timed eighth notes, so does this performance of “Master of Puppets” count as 5/8 when one eighth note is regularly 30% longer than the rest?

I feel like that isn’t a question that can really be answered completely — on the one hand, 5/8 is probably the easiest notation to read when learning how to play the song yourself, but on the other hand it’s not exactly what’s in the recording, and the shift makes a big difference in how the riff feels. If you don’t believe me, try playing the eighth notes as straight as you can, and you’ll quickly see that the sudden lurch this extra time adds to Metallica’s performance is really significant. Every time I get up and headbang to “Master of Puppets,” I get a sudden burst of adrenaline when I hear this riff. This kind of visceral reaction entirely depends on the “inexact” timing Metallica uses, and the way it upsets with the movement of my headbanging body, for its effect.

If meter is defined as how you feel the beats of a measure, the last measure of this riff is certainly not 5/8, just because it feels very different. I’m not sure I could put another set of numbers into a time signature that would work better, but I think it’s important to recognize that this rhythm has a very different shape and physical implication than a straightforward measure of 5/8.