TC Electronic Intonator

One of the most important innovations in recent studio technology is the ability to automatically correct out‑of‑tune vocals in real time. Antares have had this field to themselves with their Auto‑Tune plug‑in and ATR1 hardware unit — but now there's competition. Paul White tries out TC Electronic's version of perfect pitch in a box.

TC's new Intonator is a vocal pitch‑correction device aimed at the same sector of the market as the already highly successful Antares ATR1 hardware box. The Intonator was designed in collaboration with IVL, (the Canadian company behind the process used in the Digitech Vocalist and other products), who have a long track record in developing leading‑edge pitch‑tracking technology — clearly a valuable asset when designing a product such as this one! Vocal pitch correction is technically very difficult, because before any correction can be made, the system needs to be able to figure out the pitch of the original input. Unfortunately, voices aren't based on nice neat sine waves, and they also include unpitched components or fricatives, such as S and T sounds. Once an algorithm has been designed to extract the pitch information from a complex vocal waveform, a different algorithm has to be applied to pitch‑shift the signal, in real time, to the nearest note in the target scale. Creating natural‑sounding pitch‑shifts without all the glitching and warbling of a conventional shifter is something else IVL have a lot of experience of.

In an attempt to make the Intonator more versatile, TC have also built in a number of enhanced features, including pitch‑to‑MIDI conversion, de‑essing and adaptive low‑frequency filtering. Both analogue and digital outputs are fitted as standard, while the audio path employs 24‑bit converters, with the option of operating at 96kHz if required. There's a dithering algorithm for those needing less than a 24‑bit output, and the output bit depth can be selected as 8, 12, 16, 18, 20, 22 or 24 bits.

Housed in a standard 1U rack case, the Intonator is mains powered and uses balanced XLRs for the analogue inputs and outputs. Unlike Auto‑Tune, the Intonator has two audio channels, because one of its modes allows pitch correction to be handled in one channel while the other is dedicated to de‑essing/filtering. The more usual mode (single‑channel operation) places the de‑esser and low filter after the pitch‑correction section. Digital signals may be fed to the unit via S/PDIF, AES‑EBU or ADAT Toslink optical interfaces, the ADAT option being selectable for track pairs 1/2, 3/4, 5/6 or 7/8. MIDI In, Out and Thru sockets are fitted, along with a word clock input on an RCA phono, with a further jack provided for external control via an optional pedal. The normal sample rates are either 44.1kHz or 48kHz, but there's a double rate option that provides 88.2 and 96kHz operation. The onboard ADAT interface does not support these high rates.

The front panel looks rather more complicated than that of Auto‑Tune, but is actually very simple in operation, with a merciful absence of multi‑function buttons. There's an input gain control for the analogue input, with green and red LEDs to monitor signal present and clip, followed by the bright plasma display window and note buttons. The display is used when creating scales or programs, and also incorporates two bar‑graph meters, one of which tracks the incoming signal pitch relative to the closest note, while the other shows the amount of pitch correction being applied. Although the input metering is normally limited to just two LEDs, holding down the meter button puts up a full level meter on the display for as long as is needed to set the input level.

To the right is the Alpha Dial, a rotary encoder with an integral push switch used when editing program parameters. A button above it toggles between Scale and Setup modes, and the push switch selects either the parameter or its value for editing. A rather larger dial is used for Manual pitch correction, a facility that allows individual notes to be bent into pitch, rather like using the pitch‑bend wheel on a synth. This may be useful if just the occasional note is wrong.

In the next section along are three controls called Window, Attack and Amount. Window is used to set the pitch range within which the Intonator will try to correct the note. If a note falls outside the window, the Intonator will leave it unchanged. Window is adjustable up to 200 cents, and operates either side of the notes in the target scale. Attack sets the rate of pitch correction, to enable the most natural result to be achieved, and Amount determines by how much the pitch is corrected. With the control fully up, the Intonator attempts to get the pitch exactly right, while at lower settings, a little human error is allowed to remain. As with Attack, it's a matter of adjusting and listening to see which gives the most natural result. A non‑latching Hold button in the manual section also allows the target note to be held at the current value until the button is released.

Finally comes the Dynamics section comprising the de‑esser and the Low Cut Filter. The de‑esser applies high‑frequency cut whenever sibilant signals are detected (the sibilance‑detection frequency can be adjusted in the Setup menu), while the Low‑Cut filter removes low hum and rumble in the 55Hz to 265kHz range as set by the control knob. However, rather than just functioning as a fixed low‑cut filter, there's a switchable auto mode that monitors thinput signal. In this mode, if the input signal gets within five semitones of the filter frequency, the filter automatically adjusts itself downwards to let the sound through. Clearly this auto mode would be no use for removing loud pops, however, as the filter would politely move aside to let them through, which is why there's also a conventional fixed mode.

I mentioned earlier that there were two possible routing modes, again accessed via setup. The normal mode feeds the signal through the pitch correction, the de‑esser, then the low‑cut filter; where a digital output is being used, there's also the option to dither to lower bit depths. The second routing mode places the pitch correction in one channel and the de‑esser and filter in the other; in this mode, the low cut filter only operates as a fixed filter.

The Intonator has an impressive MIDI specification including the ability to output pitch‑correction and front‑panel control information over MIDI, where it may be recorded into a sequencer. This information may be sent and received on the MIDI Control channel, allowing MIDI to be used to control pitch directly. The input signal pitch and pitch‑bend information is also output over MIDI on a separate channel called the Pitch Channel. More common uses for MIDI include the ability to dump program information and the ability to input scale notes in real time via MIDI, though MIDI Program Change is not supported.

Operation

The Intonator has an impressive MIDI spec and comprehensive digital interfacing.The display is used when creating scales or programs; when the Intonator is actually working on a vocal, it shows two bar‑graph meters which, respectively, track the incoming signal pitch relative to the closest note, and show the amount of pitch correction being applied.

The scale types on offer are major, minor, chromatic and custom. To create a custom scale, all you need do is press the note buttons below the display (each has green status LED) to light up the notes of the scale you want. The scale is automatically saved to the Custom memory, and is retained on power‑down to be restored when the machine is restarted. It's a shame there is only one Custom memory on board, but it can be saved over MIDI, which is something. Auto‑Tune, which we reviewed back in October '98, has the facility to input notes that you specifically want the correction process to ignore, but with the Intonator, this must be done by setting the Window control such that the note to be ignored falls outside the processing window..

Vocal pitch correction is technically very difficult, because before any correction can be made, the system needs to be able to figure out the pitch of the original input.

To achieve a natural result, it's important to adjust the attack time to suit the material. If you set the attack to be too slow, the pitch may never get fully corrected before the singer moves on to the next note. Set it too fast, on the other hand, and the pitch starts to yodel in an almost quantised kind of way, though (unlike Auto‑Tune) it doesn't go quite far enough to create that wonderfully cheesy 'Believe' vocal sound that Cher condemned to death with just one record. TC say, however, that this is a deliberate aspect of the Intonator's design — it has been specifically optimised for use as a transparent pitch‑correction tool, rather than a special effects device.

Where songs have key changes, it's easiest to stop the tape, set up a new scale for the new section and then carry on; in manual mode, however, it's also possible to enter MIDI notes in real time to define the scale to which notes will be corrected. This is a particularly nice way to work if you're running your recording in sync with a sequencer. Similarly, in manual mode, you can use the front‑panelnob to bend errant notes into pitch, or connect a MIDI keyboard and use the pitch‑bend wheel to do the same job.

Those into precision surgery may prefer to play back a recording via the Intonator, record the MIDI pitch information directly into a sequencer, edit it, then use it to control the pitch of the performance. It's more fiddly than using the Auto mode, but for specific jobs where everything must be exactly right, it's a useful option to have.

What really matters is how well the pitch correction works, and as with Auto‑Tune, you'll only get great results if the vocal performance is reasonably close in the first place. I found that setting the attack rate to faster than halfway was risky, as a hint of electronic yodelling becomes noticeable on some notes, and there are occasions where the pitch‑shifted sound takes on the slightly dithery quality that pitch‑shifters in general can produce. Setting a longer attack time invariably gave the best result, and if you can use a less‑than‑maximum setting for the correction amount, so much the better. I tested the unit with a MIDI input from a keyboard and found that it worked well whether chords or single‑note lines were played. If you hold down a chord, the target scale effectively becomes the notes in that chord, while playing single‑note lines force the singing to follow that line — providing it is within the acceptance window that's been set.

Used carefully on a track that's reasonably well sung in the first place, the Intonator is capable of producing extremely transparent results.

Used carefully on a track that's reasonably well sung in the first place, the Intonator is capable of producing extremely transparent results, though having compared it side‑by‑side with my ATR1 box, I feel that the ATR1 is just a little smoother‑sounding. Furthermore, Auto‑Tune can be abused to create novel results by setting only two or three notes in a scale and then forcing whatever is sung to follow those notes, but with the Intonator, the maximum window size of 200 cents precludes this. Once the note is out of range, it will come through as originally sung.

On the plus side, the Intonator has MIDI pitch tracking built in, it has a very comprehensive digital interface that the ATR1 lacks, and it has the de‑esser and filter. I tried the de‑esser and found it to be as effective as most stand‑alone de‑essers, though it isn't quite as transparent‑sounding as the Drawmer and SPL units that only notch out the offending frequency band. It seems as though general high‑cut is applied during sibilance, and though this is a lot better than a basic full‑band de‑esser, you may still notice a slight timbral change as the de‑esser operates.

The adaptive filter is extremely transparent in operation, and even when set right up at 265Hz, there's no audible effect on a vocal line as it moves downwards to accommodate the lowest frequency in the input signal. It's a great tool for cleaning up low‑end noise, especially traffic noise and mic‑stand rumble.

Conclusion

TC have produced a very clever box that combines intelligent pitch correction with a perfectly functional de‑esser and a very useful adaptive low‑cut filter. The 96kHz option is useful to those who want to use the Intonator with high sample‑rate workstations, while the ADAT interface is convenient for processing signals that are either recorded on ADAT (or other device with an ADAT interface) or passing through a mixer with an ADAT interface. The processing delay through the box is around 15mS, which is insignificant for most vocal work, but in applications where timing is critical, at least knowing the delay figure allows you to correct for it elsewhere in the system. As you've probably guessed, automatic pitch correction isn't the magic solution for dire vocalists, but if you're faced with a nominally good take that suffers from a modest degree of poor pitching, Intonator will polish it up pretty effectively.

The Window within which the Intonator applies pitch correction can be controlled, up to a maximum of 200 cents using the control on the left here.