As regards choice of timbre, phrases in imitation are subject to the law of register. When a phrase is imitated in the upper register it should be given to an instrument of higher range and vice versa. If this rule is ignored an unnatural effect will be produced, as when the clarinet in its upper range replies to the oboe in the lower compass etc. The same rule must be followed in dealing with phrases, actually different, but similar in character; repeated phrases of different character should be scored in a manner most suitable to each.
Examples:
The Tsar's Bride 157, 161.
Legend of Kitesh 40-41.
* [No. 251.] Spanish Capriccio S.
In echo phrases, that is to say imitation entailing not only decrease in volume of tone but also an effect of distance, the second instrument should be weaker than the first, but the two should possess some sort of affinity. An echo given to muted brass following the same phrase not muted produces this distant effect. Muted trumpets are eminently suited to echo a theme in the oboes; flutes also may imitate clarinets and oboes successfully. A wood-wind instrument cannot be used to echo the strings, or vice versa, on account of the dissimilarity in timbre. Imitation in octaves (with a decrease in resonance) creates an effect resembling an echo.
Examples:
Ivan the Terrible, Act III 3.
[No. 252.] Sadko 264.
* Spanish Capriccio E.—This example is not precisely an echo but resembles one in character (cf. [Ex. 44]).