Stave Size Matters

Working on the Instrument Library – which has occupied the last few posts – I came to the point of editing staves inside instruments. That led, as it does, to clef representation; and clef representation led to the question of stave heights; and stave heights, once you look at them honestly, open onto a set of questions about what the numbers actually mean and who they serve. This is how development works: you pull on one thread and another appears. You pull that one and something else comes loose. The art is not pulling on all threads at the same time, or you end up with all yarn in one tangled clump. And when the threads start to proliferate, that is the signal to stop pulling and start architecting.

So: stave sizes. One thread at a time.

The stave space – the distance between two adjacent stave lines – is how Ooloi measures everything. Glyph dimensions, stem lengths, beam thicknesses, spacing: all of it derives from that single value, stored in millimetres. Not stave height; the space. The height is a consequence.

I spent some time recently with the rastral table. A rastrum was a pen with five nibs, drawn across the copperplate page to produce a music stave in one stroke. The finite set of available pen widths produced nine standard stave heights, numbered 0 (largest) to 8 (smallest), each associated with a particular use. The pens are gone; the vocabulary remains. When an engraver says 'Rastral 3', the meaning is immediate: 7.0 mm, standard parts, piano. No conversion required, no mental arithmetic. It encodes decades of professional judgement about what is legible at what distance for which purpose.

These values follow Gould (Behind Bars). Ross gives very slightly different numbers at some sizes – tenths of a millimetre – but Gould is the more recent authority and the more widely referenced in current practice.
Ooloi's sizing model is compositional. The base stave space propagates through a scaling chain – system, instrument, stave – where each level is a ratio against its parent. Change the base and everything follows. An ossia stave sits at two-thirds; a cue stave at three-quarters. The user works in ratios. The system reports the consequences in millimetres, with the approximate rastral equivalent alongside.

That last part is where the investigation led somewhere I hadn't originally planned. Once I had the scaling chain and the rastral table in front of me, the obvious next question was: should Ooloi simply display the effective size, or should it also say whether that size is appropriate for what the layout appears to be?

The answer, I think, is that it should. Wherever Ooloi reports an effective stave size – layout inspector, part configuration, print preview – the display will include a contextual assessment. Not just '7.4 mm (Rastral 2)' but whether that size makes sense for a flute part, or is slightly small for a piano reduction. The assessment will draw on published professional standards: MOLA puts 7.5 mm as the most readable size for orchestral parts, with anything below 7.0 mm unacceptable. The NZSO requires parts between 7.0 and 7.5 mm and rejects submissions outside that range.

The software will tell you what it knows. It will not prevent you from doing anything.
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Rastral presets will appear on the base stave size control as named starting points, and again as targets when generating parts. Three places in total; nowhere else. The vocabulary will thread through the workflow without touching the architecture. A professional courtesy, not a load-bearing wall.