what stands at zero on each of them, and why −10 and +4 are not fourteen apart
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
Pressure references are ISO 1683:2015, tables 1 and 2. Full scale and the −20 dBFS reference signal are SMPTE RP 155:2014. Alignment level is EBU R68-2000.
A decibel is always a ratio, and until it is said what the ratio is to, the number means nothing. The letter after «dB» is that statement: on dBV zero is one volt, on dBu it is 0.7746 of a volt, on dB SPL it is twenty micropascals. The same signal, the same physics, three different numbers.
This costs the most where the scales look alike. A consumer output at −10 dBV and a studio one at +4 dBu are not fourteen decibels apart but 11.8: between the zeros of those two scales lies a constant offset of 2.22 dB, because one volt and 0.7746 of a volt are not the same thing.
ISO 1683 carries the same thought to its end, setting the reference for air at 20 µPa and for water at 1 µPa, and noting itself that the same pressure under water reads 26.0 dB higher. «120 decibels» without a stated medium is not a loudness but half a sentence.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 8 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
seven carriers over a century at one scale, and what each one brought first
two shapes, twelve chords each
eight instruments at one scale · what each is about and how it sounds
how many steps the level is cut into, what a bit adds, and why floating point is not the next row