Re: Tempo

I've had a couple of private responses to this thread, and think its 
worth pointing out publicly that "tempo" and "speed" are not the same thing.

The playback /speed/ of a sequence of durations can be changed even if 
the sequence has no perceptible /tempo/.
In other words: given a sequence that is so irregular that a human mind 
can't find a perceptible tempo, multiplying each duration by some factor 
will change the (physical and perceived) playback speed.

Note too, that machine playback does not depend on (humanly perceived) 
tempo. Machines don't do chunking, they just play each individual 
duration as it comes.

All the best,
James

Am 29.03.2017 um 12:08 schrieb James Ingram:

> Hi all,
>
> I think we need to get on the same page as regards "tempo".
> This is a thorny topic, but I think we should grasp this beast by the 
> horns.
>
> For me, tempo is a term used (by humans) to say that a set of 
> sequential durations are perceived to be the same, or nearly the same.
>
> Its well known that human perception uses chunking to simplify the 
> data management. We use the term "green" to describe a particular 
> bandwidth of frequencies. According to Wikipedia, the complete visible 
> spectrum ranges from 4*(10^14)Hz (red) to 8*(10^14)Hz (violet). The 
> colours are classically chunked into 7 categories: red, orange, 
> yellow, green, blue, indigo.
>
> Similary, we have a limited spectrum of perceptible tempi.
> My metronome is calibrated from 40bpm to 208bpm (i.e.  0.66Hz to 
> 3.47Hz). Interestingly, it divides the range into 8 categories:
> 1. Largo (40-60 bpm)
> 2. Larghetto (60-66 bpm)
> 3. Adagio (66-76 bpm)
> 4. Andante (76-108 bpm)
> 5. Moderato (108-120 bpm)
> 6. Allegro (120-168 bpm)
> 7. Presto (168-200 bpm)
> 8. Prestissimo (200-208 bpm)
>
> Tempi outside this range simply don't exist. If one wants to maintain 
> a "tempo" outside this range, one typically changes tempo to a value 
> inside the perceptible range. For example, to maintain a "tempo" of 
> 4bpm, one could count at a perceived tempo of 60bpm and note each 15th 
> beat. That's cheating. Some humans perform pretty accurately like 
> that, but nobody will completely agree with a machine after a long 
> enough time.
> In real music making, performance practice (the forming of local time) 
> is infinitely more important than agreeing with a machine about 
> global, absolute time.
> (Theoretically, all machines ought to agree on the duration of 
> absolute time, but even there things are more complicated. Its 
> necessary to have a central clock that periodically tells the machines 
> what time it is.)
>
> The bottom line is that tempo is a mental phenomenon. We don't, like 
> machines, relate time to the vibration of some unchanging crystal (A 
> physical second is defined as 9 billion oscillations of a caesium atom).
> The guys who standardized MIDI in the 1980s didn't distinguish clearly 
> enough between mental (performance practice) and physical time, and 
> the Web MIDI API (latest version Dec. 2016) was right to eliminate 
> tempi (MIDI ticks) from the standard.
>
> By the way: The inability of 20th century composers to encapsulate 
> performance practice in their (paper) notation meant that they needed 
> specialist ensembles and/or inordinate amounts of rehearsal time. 
> That's very expensive, and the result is that the performance practice 
> for New Music has ceased to develop. Everything has got rather boring. 
> There have been no significant advances in the performance practice of 
> New Music for several decades...
>
> Human and machine time are very different. We should talk to machines 
> in their own language, but humans should be enabled to develop 
> performance practice. Embedding both graphics and recordings in score 
> files opens up that possibility. The development of performance 
> practices for Jazz or Ancient Music has depended crucially on the 
> availability of accurate recordings...
>
> Enough!
>
> Best,
> James
>
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