Songwriting, practice, and live music
Song Key Change Planner
Calculate modulation interval and transpose destination-section chords.
Enter planning values
Keep units, version, deadlines, capacity, and counting rules attached to the entries.
The songwriting, practice, or live-music result will appear here.
What Song Key Change measures
Calculate modulation interval and transpose destination-section chords.
Calculate the shortest signed pitch-class distance from the source key to the target and add that shift to every entered chord root modulo twelve.
The headline output is modulation plan. Read it with Source key pitch class, Target key pitch class and Source chord roots; removing those labels turns a reproducible calculation into an ambiguous number.
Preparing the entries
Take Source key pitch class, Target key pitch class and Source chord roots from the same arrangement or lyric draft. If Source key pitch class belongs to a later revision, update the companion entries or save the two versions as separate cases.
Keep the stated units beside Source key pitch class and Source chord roots. The Song Key Change form does not infer a missing unit, convert an unstated counting convention, or know which draft is current.
How to read modulation plan
Pitch classes identify roots without spelling. The same number can require a sharp or flat name depending on key, voice leading, and notation context.
Compare modulation plan with the score, demo, lyric sheet, and tempo map. An arithmetically correct modulation plan can still conflict with a confirmed constraint outside the model.
A controlled check
Run the defaults once, note modulation plan, and then change only Source key pitch class. Before calculating again, predict whether modulation plan should rise, fall, or remain unchanged.
Restore the original Source key pitch class and confirm that +2 semitones returns. This exposes stale Song Key Change entries and keeps the example useful when the working plan changes.
Worked example from the starting values
The published example uses Source key pitch class = 0; Target key pitch class = 2; Source chord roots = 0 5 7. With those entries, the calculator returns +2 semitones: Shortest signed modulation interval.
Keep the Song Key Change example as a quick functional check. Replace Source key pitch class, Target key pitch class and Source chord roots only after it reproduces, and never copy its answer into a project that uses different units or assumptions.
A mistake to avoid in Song Key Change
Transposing roots does not automatically preserve playable voicings, melodic range, or a singer's comfortable register.
Check Source key pitch class, Target key pitch class and Source chord roots for copied totals, mixed revisions, hidden allowances, and early rounding. Any of those errors can make modulation plan look plausible without being reproducible.
Putting the number to work
Use the shifted roots as a harmonic sketch, then choose spellings and voicings in the actual target key.
The Hook Repetition Calculator can answer the next nearby question, but carry over only values that describe the same version of the project.
Defining the calculation boundary
Write down what Source key pitch class begins and ends, and whether Source chord roots includes every component the project treats as part of the calculation. A boundary for modulation plan stated in advance prevents quiet changes during review.
List any deliberate exclusions beside modulation plan. If an omitted pause, fee, route leg, rehearsal task, spare channel, or musical event later becomes relevant, add it explicitly and rerun Song Key Change rather than adjusting the answer by memory.
Use the same inclusive or exclusive counting rule for Source key pitch class and Source chord roots in the source document and this form. Start bars, final days, last acts, between-song pauses, and between-set breaks deserve particular attention when reporting modulation plan.
Testing another scenario
Save the first modulation plan as a baseline rather than overwriting it. Change one uncertain assumption—such as source chord roots—and label the alternative clearly.
The difference shows how sensitive modulation plan is to source chord roots. For source chord roots, that comparison is more informative than adding display precision to an uncertain source value.
Precision and reporting for modulation plan
Keep the calculator's underlying precision while modulation plan feeds another calculation, but report only digits supported by Source key pitch class and the other source entries. Extra decimals cannot repair a rough estimate.
If modulation plan must become a whole count, clock time, purchase quantity, or scheduled commitment, apply the practical rounding rule at the final handoff and record which direction was used.
When sharing modulation plan, include a plain-language label and the relevant unit or clock basis. A reader should not need to reopen Song Key Change merely to learn what +2 semitones represented in the saved example.
Limits of the estimate
Musical intent still has to be heard and revised when interpreting modulation plan. Song Key Change represents Source key pitch class, Target key pitch class and Source chord roots; it cannot observe the surrounding room, performer, audience, vehicle, equipment, or agreement.
If modulation plan touches safety, contracts, electrical work, wireless operation, or local rules, treat it as preparation for the appropriate qualified or responsible person—not as approval.
Keeping a reproducible note
Record Source key pitch class, Target key pitch class and Source chord roots, modulation plan, the date, and the plan version. Mark whether Source chord roots is estimated, measured, or confirmed.
If a decision based on modulation plan changes, keep the earlier case. The Song Key Change history then shows whether the difference came from the model, a revised input, or a changed objective.
Questions about song key change
What does Song Key Change Planner calculate?
It calculates modulation plan from Source key pitch class, Target key pitch class, Source chord roots. Calculate the shortest signed pitch-class distance from the source key to the target and add that shift to every entered chord root modulo twelve.
What should I verify before using the modulation plan?
Confirm that Source key pitch class, Target key pitch class, Source chord roots come from the same plan version and follow the units or counting convention shown on the form.
What is the main limitation of Song Key Change?
Pitch classes identify roots without spelling. The same number can require a sharp or flat name depending on key, voice leading, and notation context.