more, since tone generation via the *CPU* is an exclusive task, you cannot do anything else on or off screen while the sound is playing, so in order to perform other functions while sound is generated by using the *CPU*, you will also have to program in *Machine Code*, or –assuming you have the *Accelerated* version or a *Pi Zero* installed– use the audio playback facilities described in the last section of this chapter (the latter working independently of whatever the ZX Spectrum Next is doing). Try programming tunes in for yourself – start off with fairly simple ones like *Three Blind Mice*. If you have neither piano nor written music, find a very simple instrument like a tin whistle or a recorder, and work the tunes out on that. You could make a chart showing the pitch value for each note that you can play on this instrument. Type: ``` FOR n=0 TO 1000: BEEP .5,n: NEXT n ``` This will play notes as high as it can, and then stop with error report **B Integer out of range**. You can print out **n** to find out how high it did actually get. Try the same thing, but going down into the low notes. The very lowest notes will just sound like clicks; in fact the higher notes are also made of clicks in the same way, but faster, so that the human ear cannot distinguish them. Only the middle range of notes are really any good for music; the low notes sound too much like clicks, and the high notes are thin and tend to warble a bit. Type in this program line: ``` 10 BEEP .5,0: BEEP .5,2: BEEP .5,4: BEEP .5,5: BEEP .5,7: BEEP .5,9: BEEP .5,11: BEEP .5,12: STOP ``` This plays the scale of *C major*, which uses all the white notes on the piano from *middle C* to the *next C* up. The way this scale is tuned, is exactly the same as on a piano, the so-called *even-tempered tuning* because the pitch interval of a *semitone* is the same all the way up the scale. A violinist, however, would play the scale very slightly differently, adjusting all the notes to make them sound more pleasing to the ear. He can do this just by moving his fingers very slightly up or down the string in a way that a pianist can't. The *natural scale*, which is what a violinist would play, comes out like this: ``` 20 BEEP .5,0: BEEP .5,2.039: BEEP .5, 3.86: BEEP .5,4.98: BEEP .5,7.02: BEEP .5,8.84: BEEP .5,10.88: BEEP .5,12: STOP ``` You may or may not be able to detect any difference between these two; some people can. The first noticeable difference is that the third note is slightly flatter in the *naturally tempered scale*. If you are a real perfectionist, you might like to program your tunes to use this natural scale instead of the even-tempered one. The disadvantage is that although it works perfectly in the *key* of *C*, in other *keys* it works less well – they all have their own natural scales – and in some *keys* it works very badly indeed. The *even-tempered scale* is only slightly off, and works equally well in all keys. This is less of a problem on the computer, of course, because you can use the trick of adding on a variable **key**. Some music – notably Indian music – uses intervals of pitch smaller than a *semitone*. You can program these into the **BEEP** statement without any trouble; for instance the *quartertone* above *middle C* has a pitch value of **.5**. You can make the keyboard beep instead of clicking by: