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Playing an arpeggio

by Richard Russell, December 2014

If you want to play a sequence of short, rising, notes (for example from the chromatic scale) the most obvious way is something like this:

```        ENVELOPE 1,1,0,0,0,0,0,0,126,-4,0,-1,126,0

pitch = 100
FOR note = 0 TO 19
SOUND 1, 1, pitch, 2
pitch += 4
NEXT```

The problem with this technique is that when each note is sounded the previous one is suddenly truncated, even though an ENVELOPE was used to give it a long release time. This happens because all the notes are played on the same channel, and it gives the end result a 'staccato' effect.

To reduce this effect you can take advantage of the multiple SOUND channels available, for example the first note can be played on channel 1, the second on channel 2 etc.:

```        ENVELOPE 1,1,0,0,0,0,0,0,126,-4,0,-1,126,0

SOUND 2,0,0,2
SOUND 3,0,0,4
pitch = 100
FOR note = 0 TO 19
SOUND (note MOD 3) + 1, 1, pitch, 2
IF note<17 SOUND (note MOD 3) + &1001, 0, 0, 4
pitch += 4
NEXT```

Each note is played for two 'sound periods' (normally 1/20 second each) and then allowed to decay for 4 'sound periods'; this is achieved by setting the 'hold' bit (H). To ensure that the notes are correctly 'interleaved' an initial period of silence is played on channels two and three, of 2 and 4 'sound periods' respectively.

If you want to improve the effect even further, you can switch SOUND channel 0 from its normal 'noise' functionality to become a fourth tone channel:

```        *TEMPO 133
ENVELOPE 1,1,0,0,0,0,0,0,126,-4,0,-1,126,0

SOUND 1,0,0,2
SOUND 2,0,0,4
SOUND 3,0,0,6
pitch = 100
FOR note = 0 TO 19
SOUND (note MOD 4), 1, pitch, 2
IF note<16 SOUND (note MOD 4) + &1000, 0, 0, 6
pitch += 4
NEXT```

(My apologies to musical purists who may not feel that this is an arpeggio in the strict sense.)