What is a Harmonizer?
A harmonizer is a type of pitch shifter that combines the “shifted” pitch with the original pitch to create a two or more note harmony. In digital recording, pitch shifting is accomplished through digital signal processing. Older digital processors could often shift pitch only in post-production, whereas many modern devices using computer processing technology can change pitch values virtually in real time. Whenever you hear ultra tight vocal harmonies that sound “too perfect” you are listening to a harmonizer at work. However, sometimes it is not that obvious. Harmonizers can thicken, detune and add effects to instruments and can, for the creative, make very strange effects out of any audio material.
Digital Pitch Shifter
The first digital pitch shifter that did not change the timing was Eventide H910 Harmonizer, introduced in 1974. Back then music producers used it mainly as an effect, rather than to correct out of tune singers as it is common today. A harmonizer can, of course, create harmonies. There is no easy way to automate parameters on a hardware device as with modern plugins, so to correct individual notes, one will have to adjust the pitch knob manually while the mix plays. Or to process a copy onto another track, then mute the original track in muted places. This is obviously tedious compared to the luxury we enjoy today with DAW software.
Double Tracked Vocals
One common use for a harmonizer is to simulate the effect of double-tracked vocals. In the 1960`s, it was common for singers to sing the same part twice onto different tracks to enhance the vocal, making it more rich-sounding. This isn’t a great vocal effect for intimate ballads, but it is common with faster pop tunes. Double tracking is also done with guitars and other instruments, not just voices. One difficulty with double-tracking is the singer or musician has to perform exactly the same way twice. Small timing errors that might pass unnoticed on a single track become much more obvious with two tracks in unison.
Automatic Double Tracking
A harmonizer offers a much easier way to create the effect of double tracking from a single performance. The original and shifted versions are mixed together, with both typically panned to centre. This is “automatic double-tracking”, or ADT for short. You can also use a harmonizer to add a widening effect by panning the original and shifted versions to opposite sides. Either way, the harmonizer is typically set to raise (or lower) the pitch by 1 or 2 percent. A larger shift amount adds more to the effect, but eventually, it sounds out of tune.
One big advantage of using a harmonizer effect for ADT rather than simple delay is to avoid the hollow sound of static comb filtering. Since effective delay through a harmonizer is constantly changing, the sound becomes full rather than thin and hollow. Rolling off the high end a bit on the harmonizer`s output keep blended sounds even smoother and less affected.
Additional Resources & Source Texts
https://books.google.rs/books?id=DX-mRhkJL74C&dq=harmonizer%20audio%20effect&source=gbs_navlinks_s
