Complex sentence: It is still possible for two sounds of indefinite pitch to clearly be higher or lower than one another, for instance, a snare drum invariably sounds higher in pitch than a bass drum, though both have indefinite pitch, because its sound contains higher frequencies.
Split into simpler sentences: It is still possible for two sounds of indefinite pitch to clearly be higher or lower than one another. For instance, a snare drum sounds higher pitched than a bass drum though both have indefinite pitch, because its sound contains higher frequencies.