First write the degree of the required interval, that is, first write the basic framework of the interval, that is, without adding any ascending and descending marks.
Distinguish the name of the interval, and then compare whether the difference with the required interval is large or small.
Expand or reduce the interval according to the difference, and adjust it with the diacritic mark. Be careful not to change the tone given in the title!
It is required to form a minus fifth interval on the be1 sound. The first step is to find the be1 sound:
, and write the basic framework of the fifth interval:
In the second step, the name of the
interval to be distinguished is the augmented fifth interval, which is one whole tone different from the required minus fifth interval (and the crown is raised by one whole tone).
The third step, don't move the be1 sound! Add a double flat mark before the crown sound of the frame:
. At this point, the exercise is complete.
--Source: Moon Musical Instruments Community
--https://bbs.moonyueqi.com/forum.php?mod=viewthread&tid=1963