Original Synth

by Brian Kennerley

 

Issue 31

Jan/Feb 88

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Bryan Kennerley will turn your keyboard into a unique sound synthesiser complete with light show

The sound capabilities of the Atari 8-bits are seldom held in high repute by any but the most avid Atari freaks, but surely the fact that a version of the POKEY chip (which is the heart of Atari sound generation) is responsible for the music on some top coin-op games, including Gauntlet, means there is a great deal of potential hidden away somewhere. Hopefully, this program will help realise some of that potential.

ORIGINAL SYNTH utilises the Atari's 'volume only' method of sound production. A full explanation of this is given in the book De Re Atari but here is a brief explanation to help you understand how the program works. You should be familiar with the BASIC SOUND command, if not you can look it up in many reference books or the BASIC manual. One of the parameters that may be set is 'distortion'.

If an odd distortion number is used with zero pitch and positive volume, a 'click' will be heard. The volume of the click will be equal to the difference between the previous and the new volume. For example, if you specify volume 0 and then volume 15, the resultant volume will be 15. If you then specify 15 again, the resulting volume be 0 (15 15). If a great many of these clicks are produced in succession, a musical tone can be produced. From BASIC only a low buzz can be produced but when using machine code, the loop must be slowed down since at full speed only dogs would be able to hear it! Original Synth makes use of this feature to produce some very interesting sounds.

THE DISPLAY

When the program is RUN, you are shown a graphical view of the ADSR. This is how the volume of the note changes as the note is played. Unless you have changed anything, the volume will start off at full, decay to half volume, stay at half for a while and then fade away to silence. This can be altered to produce special effects but more about that later. Every calibration on the ADSR display is equal to one second of real time.

If you press 'V', the display will change to show the current waveform. The waveform controls how the note actually sounds. For example, brass instruments typically produce a triangular waveform. This program cannot synthesize an instrument exactly, however, since the waveform of an instrument varies as the note is played but it can give an approximation of different types of instrument.

THE MENU

The lower half of the screen shows a menu of options. I will explain each option in order:

Sound Type When this is set to FULL the ADSR is enabled. When set to PURE the volume remains constant and the note is purer.

Distortion When enabled the screen is still displayed as the notes are played, resulting in a more fragmented, less musical, tone.

Light Show When enabled, each note is accompanied by coloured lines moving up or down the screen.

Configure If you find that you are using a certain combination of waveform and ADSR frequently, choose this option to save the combination to disk. When you next run the program, that combination will automatically load.

View xxxx Scrolls between the ADSR and waveform display.

Edit Edits either the waveform or ADSR, depending on which is currently displayed. Note that in editing mode the cursor is only one Graphics 8 pixel and may be difficult to locate.

For Waveform Editing, move the flashing cursor around the screen with joystick 1 or the cursor keys and alter a point with the fire button or by holding the Return key. To alter the length of the waveform, position the cursor and hold the space bar. Shortening the waveform generally makes all notes higher and lengthening it lowers all notes. This is not always the case though, since altering the number of peaks present may counteract this effect.

ADSR Editing takes a different form to the waveform because there are 512 possible points for the cursor. The joystick and cursor keys move the cursor 1 point at a time while TAB and SHIFT + TAB move the cursor 20 points right or left respectively. Holding the fire button or Return key plots a point after which the computer joins the points with a line. Up to 64 points can be plotted at any one time. Holding space will delete a point providing the cursor is on a point previously set. This can be determined by the Point Set message on screen which will show whether the point at which the cursor is residing has been set.

I/O After choosing which type of I/O you require, you will be presented with a directory of waveforms or ADSRs as appropriate. Choose which file you want by typing its number. If you are saving a new file you will be prompted for a filename. Just type the name and NOT the "D:" or extender. Pressing the Escape key will abort the operation at any time before the file number is chosen. Be careful! The program is only protected against the 'FILE NOT PRESENT' error and no other disk error is accommodated such as 'DISK FULL'.

PLAYING MUSIC

This what all that editing is for! Press START to enter music mode and the computer becomes a 3 octave piano keyboard as shown in Figure 1. SPACE is the lowest note and RETURN is the highest. Z-INV and Q-RET are the 'white' notes while S-; and 1-DEL are the 'black' notes. Pressing OPTION at any time will return to the main menu. The notes played by this keyboard will sound according to how you have set the waveform and ADSR. I have provided several examples which you can load in from your disk, but you are free to design as many as you wish!

I have found that playing music with this program has helped me understand the layout of the piano keyboard and the intricacies of sound shaping. As an added bonus it has improved my finger/keyboard coordination and so increased my typing speed and accuracy considerably. I hope it will bring you enjoyment and benefit in a similar way.

AtariLister - requires Java

 

AtariLister - requires Java

TYPING IT IN

You will need a disk with at least 250 free sectors and it is recommended that you start with a freshly formatted disk as this can be used to autoboot Original Synth.

1. Type in listing 1, checking it with TYPO 3, and save it with the filename D:CREATOR.BAS

2. Type in listing 2, again checking it with TYPO 3, and save it with the filename D:SYNTH.BAS.

3. Ensure that your disk remains in drive 1 and is not write protected and then load and RUN D:CREATOR.BAS. This will create an AUTORUN.SYS and several other DATA and support files (13 in all) and then will the run SYNTH.BAS

4. CREATOR.BAS need only be RUN once, after which you may either auto-boot the disk or type RUN "D:SYNTH.BAS" whenever you wish to use the program.

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