This is a truly distinctive and profoundly resonant guitar tuning, famously employed by the progressive metal band Tool in their seminal songs 'Parabol' and 'Parabola'. It represents a radical departure from standard tuning, crafting an expansive soundscape ideal for generating heavy, percussive riffs and intricate, often dissonant, harmonic textures. The defining characteristics of this tuning are the remarkably low pitches of the 6th, 5th, and most notably, the 2nd strings, with the latter dropping an entire octave below its standard pitch.

Technically, the open strings are tuned to B1-E2-D3-G3-B2-E4. When compared to the familiar E-A-D-G-B-e standard tuning, this arrangement sees the two lowest strings (6th and 5th) each lowered by a perfect fourth, resulting in a low B and E. The most dramatic alteration occurs on the 2nd string, which is pitched a full octave down from B3 to B2. Intriguingly, the 4th, 3rd, and 1st strings remain at their standard pitches of D3, G3, and E4, respectively.

The unique sequence of open strings B-E-D-G-B-E offers a complex harmonic palette. While it does not readily form a simple major or minor triad when strummed openly, it presents a host of compelling intervals. The lowest three strings (B1-E2-D3) establish a powerful, often dissonant, foundation that can create immense sonic weight. The upper register, comprising D3-G3-B2-E4, contains elements of a G major triad (G-B-D) if considering the D3, G3, and B2 (an octave lower B), with the E4 adding an extended tonality. This wide voicing and unusual string relationships facilitate rich, ambient chords, drones, and the signature thick sound synonymous with Tool's musical style.

Chords that become particularly accessible or take on novel voicings include robust low fifths (power chords) achievable across the 6th, 5th, and 4th strings. For instance, a simple two-finger shape at the same fret on the 6th and 5th strings will produce a perfect fifth, making heavy, chugging riffing remarkably fluid. The unusual, deep interval provided by the B2 on the 2nd string also unlocks possibilities for distinctive arpeggios, melodic lines, and chord voicings that are simply unachievable in standard tunings. The extremely low overall pitch mandates a careful selection of string gauges to ensure proper tension and intonation, especially for the dramatically down-tuned 2nd string.

How to Tune

When transitioning to Tool's Parabol/Parabola tuning from standard E Standard (E-A-D-G-B-e), it is crucial to proceed with caution and precision. Given the substantial drops on several strings, particularly the 2nd string, it is highly recommended to use heavier gauge strings than your standard set. This will help to maintain appropriate tension, prevent excessive floppiness, and ensure stable intonation. For any string movement exceeding 4 semitones (either up or down), a different string gauge is strongly advised for optimal playability and instrument health.

• 6th String (Low E): Tune down 5 semitones to B1. Due to this significant drop, a heavier gauge string for the 6th string is recommended to maintain adequate tension.
• 5th String (A): Tune down 5 semitones to E2. Similar to the 6th string, a heavier gauge string for the 5th string would be beneficial to prevent slackness.
• 4th String (D): Keep as is; no change (0 semitones). This string remains at its standard pitch of D3.
• 3rd String (G): Keep as is; no change (0 semitones). This string remains at its standard pitch of G3.
• 2nd String (B): Tune down 12 semitones to B2. This is an extreme drop of a full octave. To ensure this string is playable and maintains any reasonable tension, a much heavier gauge string is absolutely essential. Failure to do so will likely result in an unplayable, extremely slack string.
• 1st String (High E): Keep as is; no change (0 semitones). This string remains at its standard pitch of E4.