Here's the third part of Clive Gifford's series on Amstrad CPC464 noise capabilities
Now that the envelope commands have been covered, there is one final area I would like to mention and that is your Amstrad's ability to generate white noise.
White noise is the basis of ail the explosions, gunshots and drumbeats you hear on your Amstrad. White noise allows a whole new range of sounds to be created, sounds which don't have a musical note for their basis.
How do you obtain the noise channel? Firstly, you must switch off the pitch parameter of the sound statement, then by adding a number between 1 and 15 as the seventh number on your SOUND statement, you choose one of the different types of white noise available.
Putting a number of the different noises in a loop to be played one after another creates an interesting effect. If you play them in reverse order (from 15 to 1) with a duration of a half or a third of a second, you get quite a good imitation of the sea breaking on the shore.
The noise channel can be used on its own, as suggested above, but it can be and often is more effective when used in conjunction with one of the sound envelopes. Below are two different effects found when white noise is shaped by an envelope.
10 ENV 1,100,4,8
20 ENT 1,20,-15,40
30 SOUND 1,0,800.1,1,1,12
10 ENV 1,20,4,2
20 SOUND 1,200,100,1,1,0,5
30 GOTO 20
The mini-synthesiser demonstrates a number of the features we have discussed over the three articles. The top row of keys, excluding the ESC key, all play a different note. The KEY DEF commands in line 290 allow the keys on the right of the top row (DEL, CLR etc) to be used. On pressing the ESC key twice, the computer resets these keys to their original values.
The 14 keys play the basic notes of the middle and the upper first octave. The data in line 280 corresponds to the Amstrad manual's music octaves and this information is stored in the array M(X). You must select the sound you require from the choice of Piano, Peeow (rather like synthesised drums), Organ (the basic, unaltered sound of the Amstrad's sound generator) and Space. Use ‘Q' , 'W' , 'E' and ‘R' to select your sound and then play away!
As a sound key is pressed, a tone and/or volume envelope is selected. From looking at lines 100 to 130 and lines 300 to 340, you can see which envelope causes which effect and naturally, these envelopes can be taken from the program and used in your own programs.
Lines 150 to 170 play the note which lasts for just under one-third of a second. I first tried to keep the duration far shorter, to maintain more control over the sounds and the speed they are played, but I soon found that the quality of the envelopes deteriorated when adjusted to smaller durations. The end result is a compromise which produces some reasonable effects.
The rest of the program is concerned with collecting your input and with providing the screen display.
Home Computing Weekly #108
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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.