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Chapter 17 - Qbasic Tutorial

If you just need a beep in your program, you can use BEEP:

INPUT "Press Enter to hear a beep", A$

SOUND lets you play a beep and tell it how high or low the beep will be, and how long it will last. This program makes a 1000Hz beep for about 1 second:

 SOUND 1000, 18

SOUND is good for making sound effects. Here's a bomb dropping:

 FOR I = 4000 TO 1000 STEP -5

If you want to play a song, PLAY is exactly what you need. Try this:

 PLAY "e8 d8 c8 d8 e8 e8 e4"

PLAY is like a little programming language inside of QBASIC. "e8" means play an eighth note "e". If you are familiar with sheet music, this will make sense. Here's a scale:

 PLAY "c8 d8 e8 f8 g8 a8 b8 > c4"

The ">" greater than sign means "go up one octave". There are many more special commands in PLAY. Check the QBASIC help for a list of all of them.

PLAY and Triplets

Here's a familiar tune that uses a trick to do triplets.

 PLAY "T180 <d8d8d8 T120 g2>d2"
PLAY "T180 c8<b8a8 T120 >g2d4"
PLAY "T180 c8<b8a8 T120 >g2d4"
PLAY "T180 c8<b8>c8 T120 <a2>"

Since PLAY doesn't do triplets, you have to modify the tempo to get the right rhythm. PLAY begins with a default tempo of "T120" which means 120 quarter notes per minute. In the above song, we switch to T180 which is the triplet tempo for T120. By multiplying our tempo by 1.5, we get the triplet tempo. When the triplets are done, we switch back to the regular tempo. You can see in the above example that we switch back and forth between the main tempo (T120) and the triplet tempo (T180) several times as needed.

As with everything, there's more than one way to do triplets. 8th note triplets can also be called 12th notes, like this:

 PLAY "<d12d12d12g2>d2"
PLAY "c12<b12a12>g2d4"
PLAY "c12<b12a12>g2d4"
PLAY "c12<b12>c12<a2>"

Using this technique, 16th note triplets are 24th notes, etc.... You just multiply the note value by 1.5 instead of changing the tempo.

Each of these techniques has its advantages and disadvantages. The tempo-changing technique uses more space, but the notes retain their values. The 12th note technique is more compact, but not as easy to understand. Which one you use is up to you. Just make sure the next person to read your code understands what you are doing. Comments are a good idea.

Category: Qbasic Tutorial | Added by: JPSor (2009-02-26) | Author: JPSor
Views: 1528 | Rating: 4.0/2 |

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