Pitch is the frequency of the note. Tone is the accompanying harmonics or overtones which give the sound of the voice/instrument its distinctive quality. Timbre is a French word meaning (postage) stamp (usually) - in the context, timbre designates those qualities of tone that make a "voice" or instrument distinctive - you can tell it's Bing Crosby by the timbre of his voice, not by the tone - it
might be Dick Haymes otherwise