Is this the right way to use midiFreq?

gistfile1.txt

// An ascending sinOsc glissando using a line ugen.
var synth = flock.synth({
    synthDef: {
        ugen: "flock.ugen.sinOsc",
        freq: {
            ugen: "flock.ugen.xLine",
            rate: "control",
            duration: 1.0,
            start: flock.midiFreq('a'),
            end: flock.midiFreq('d')
        },
        mul: 0.25
    }
});