I regularly use two simple methods for emphasizing a melody when playing a piece of music on only one synthesizer keyboard. Since the accompaniment – be it sustained chords or arpeggios – will obviously be played with the left hand, and the bass on the pedalboard, the issue concerns the right hand. First, regarding the instrument itself, there is the ability to use a parameter that brightens the upper end of the keyboard. On Dave Smith Instruments synthesizers the parameter is called Key Amount. It is an adjustable knob that allows a wide range for the effect. As you ascend the keyboard, the filter cut off frequency gradually opens up, brightening the sound. To state the obvious, this means that the lower notes of the keyboard – where the accompaniment is being played – is darker. This is already perfect for emphasizing a melody. Hence, the chords/arpeggios are of one filter setting, while the melody is of a brighter – and if you wish – a much brighter filter setting.
This effect achieved through the Key Amount is often sufficient by itself to keep a melody from being murkily buried in its accompaniment. But a musical moment may not be best served by using a generous amount of this effect; it may require only a subtle use of it, and yet, the melody may still need to be additionally emphasized. The second method that I use is that of playing the melody at certain climactic points in double octaves, as is often done on piano. This playing in double octaves cuts through even the densest accompaniment and can also have all sorts of interesting effects, depending on the type of patch being used.
These two methods together – using the Key Amount parameter and playing the melody in double octaves – bring clarity and definition to what could otherwise be a dense and hazy sound with poorly defined musical elements.