This month, we move on to putting the sort of intervals encountered in the Pitch Tuner program (E&MM Sept 83) to work in a more obviously musical context, namely a program for teaching musical scales.

The Scales program randomly plays choices of 9 different scale types in all possible keys, ie. major, natural minor, harmonic minor, melodic minor, Dorian mode, whole tone, pentatonic, chromatic, and bagpipe. Bagpipe? Well, just for fun (and for keeping that old pitch acuity up to scratch), we've also included a few Scottish Highland bagpipe scales, which, in keeping with the instrument itself, isn't 100% in tune with the developments of Western music. In fact it's decidedly out-of-tune, as the C and F in this scale are about a quater tone sharp! However, there is a somewhat less banal motive behind including this scale in the program. The Bagpipe scale is so obviously out-of-tune that even a tone-deaf student is sure to recognise it, which means that the student should get a pleasant bit of positive reinforcement every time Bagpipe reappears, and that can only help to encourage the student in his or her scale recognition endeavours.

Though the inclusion of the natural minor scale is somewhat unconventional in the context of contemporary music education, we feel that the extensive use of this scale in jazz and rock music, and its derivation from the Ionian mode, warrants its inclusion. Some history on the evolution of scales might help at this point.

Scale History

The scales that we're all forced to practice till they're streaming from our fingertips like bath water have their beginnings in the 'church' modes that dominated European music for eleven hundred years. Thus, the Aeolian mode became our minor scale, and the Ionian mode, the major scale. It's amusing to reflect that, of the two modes that survived the test of time, the Ionian had been dubbed the 'wanton mode' (modus lascivus) on account of the way it secretly crept out of nunneries and monasteries into the evil outside world of the 12th century! Though the Dorian mode is no longer an extant scale, we've also included it in Scales for the simple reasons that a) it was popular in plainsong and early harmonised music, b) much folk music is still modally based, and c) it represents a near relation to the natural minor scale in that its particular flavour is derived from a sharpened 6th step.

(Click image for higher resolution version)

These modally - derived scales subsequently went through certain modifications to suit developing compositional styles. The harmonic minor scale arose from the need to make the transition from leading note (the 7th step of the scale - G in the case of A minor) to key note more conclusive in a harmonic context. As a result, the leading note was sharpened (G sharp in the case of A minor), thereby forming the harmonic minor scale. Unfortunately, this change created problems for singers, because the interval between the 6th and 7th steps (a minor 3rd - F to G sharp in the case of A minor) was more characteristic of Middle Eastern music than Western music. The problem was solved by sharpening the F as well, producing a smoother melodic progression, this form being known as the melodic minor scale. However, this is done only on the ascending part of the scale, the natural minor being preserved for the descent.

Choosing a response is simply a matter of using the UP and DOWN cursor keys and pressing RETURN. If your response is judged to be in keeping with what was played, you'll receive a 'Right!' message and be moved on to the next scale; if incorrect, 'Wrong!' will appear and the scale will keep on playing until the correct response is delivered. By that ploy, the scalesperson is forced to learn the identity of scales however unsure he or she may be at the start. The ESCAPE key serves the same function as elsewhere in this chapter, and it can also get you out of an embarrassing confrontation with those bagpipes!

Workings

The main areas of interest in this program are those that play the scale and wait for the player's answer. However, 'areas' is a bit of a misnomer in that it implies things in more than one place. The point is that the program has to 'play' and 'wait' concurrently, since the scale plays on until an answer is received. A programmer without an understanding of the BBC Micro's sound queue system would probably use a loop which checked for a keypress before ending each sound request. This would work since the scale plays quite fast, but, in a general application where the sounds could be any duration, the delayed keyboard response would be very poor.

The easiest solution is to use a loop as before, but only send a sound request if there is room on the queue for it ie. if the operating system can handle it without making the program wait. That's the function of PROCplay between lines 710 and 830. The other side of the program is the choosing of scales and keys (line 350 onwards), with the character strings on lines 1100 to 1180 determining the steps of the various scales.

From 'Creative Sound on the BBC Microcomputer' by David Ellis and Chris Jordan - to be published by Acornsoft in the autumn.