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Almathera Ten Pack 3: CDPD 3
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Almathera Ten on Ten - Disc 3: CDPD3.iso
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ab20
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protrack.lzh
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tempocalc.txt.pp
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tempocalc.txt
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Text File
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1995-03-17
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1KB
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26 lines
Protracker CIA (Complex Interface Adapter) Timer Tempo Calculations:
--------------------------------------------------------------------
Fcolor = 4.43361825 MHz (PAL color carrier frequency)
CPU Clock = Fcolor * 1.6 = 7.0937892 MHz
CIA Clock = Cpu Clock / 10 = 709.37892 kHz
50 Hz Timer = CIA Clock / 50 = 14187.5784
Tempo num. = 50 Hz Timer*125 = 1773447
For NTSC: CPU Clock = 7.1590905 MHz --> Tempo num. = 1789773
To calculate tempo we use the formula: TimerValue = 1773447 / Tempo
The timer is only a word, so the available tempo range is 28-255 (++).
Tempo 125 will give a normal 50 Hz timer (VBlank).
A normal Protracker VBlank song tempo can be calculated as follows:
We want to know the tempo in BPM (Beats Per Minute), or rather quarter-
notes per minute. Four notes makes up a quarternote.
First find interrupts per minute: 60 seconds * 50 per second = 3000
Divide by interrupts per quarter note = 4 notes * speed
This gives: Tempo = 3000/(4*speed)
simplified: Tempo = 750/speed
For a normal song in speed 6 this formula gives: 750/6 = 125 BPM
Lars "ZAP" Hamre/Amiga Freelancers 1990