Pitch and Time Manipulation

   By Sarah C   Categories: Audio EquipmentAudio SoftwareGeneral

It is often useful to be able to select an audio file or clip and change its pitch or its length/tempo. Pro Tools provides an AudioSuite plug-in, Time Shift, for exactly these purposes.

So why would you want to pay out extra for an AudioSuite time compression/ expansion and pitch-shifting plug-in when Pro Tools already includes those tools? The reason is that the standard Pro Tools plug-ins have restricted capabilities compared with the ‘premium’ plug-ins that you pay extra for. These will allow you to make greater changes of duration and tuning (and modify longer audio files) with less distortion and fewer digital artifacts.

There are lots of alternatives to choose from. For example, SoundToys offers Speed, which lets you change the pitch or the length of your audio files by simply grabbing a knob and rotating it. Serato offers Pitch ‘n Time, which lets you alter pitch and tempo graphically or numerically and has a Varispeed mode, where altering the tempo also alters the pitch. These have both been around for a long time and offer significant improvements compared with the basic Pro Tools plug-ins.

Avid X-Form

Avid’s X-Form (see Figure 9.57) is one of the highest-quality duration-and-tuning tools available for the Pro Tools platform.

The user interface is simple enough to operate with everything laid out logically and labeled clearly. You can either use the rotary controls to set the time or pitch shift amounts or simply type in the amounts using your choice of Bar|Beats, minute:seconds, feet:frames, time code, or samples. The gain control lets you lower the input level by up to 6 dB to avoid clipping in the processed signal.

X-Form lets you alter audio files by even larger percentages with even fewer undesirable artifacts than most of its rivals: it can process files within a range of 12.5 to 800 percent of the original length or one-eighth to eight times the original duration. It can pitch shift audio up or down by three octaves, even on polyphonic material—and with proper formant correction so that the audio sounds completely natural.

X-Form provides a choice of two time-stretching/pitch-shifting algorithms: the Monophonic algorithm for working with solo instruments or vocals, and the Polyphonic algorithm for use on audio that contains chords—or a stereo mix. Also, when used with the transient sensitivity control, X-Form allows you to compress or stretch drum loops and other percussive material without losing crucial attack transients. I have compared X-Form with most of its competitors and it definitely sounds better.

NOTE

Part of X-Form’s processing relies on separating ‘transient’ parts of the sample from ‘nontransient’ parts. Transient material tends to change its content quickly in time, as opposed to parts of the sound that are more sustained. Sensitivity is only available when polyphonic is selected as the audio type. For highly percussive material, lower the sensitivity for better transient detection, especially with the rhythmic audio setting. For less percussive material, a higher setting can yield better results. Experiment with this control, especially when shifting drums and percussive tracks, to achieve the best results.

9.57

9.57 Avid X-Form

AVID X-FORM VERSUS TIME SHIFT

I asked Avid to explain the differences between the standard Time Shift plug-in and the new X-Form plug-in. Here is what I was told: ‘While both Time Shift and X-Form offer time compression/expansion and pitch shifting with high-quality results, there are a few key reasons why X-Form outshines Time Shift. The main thing that separates Time Shift from X-Form is the quality of the processed file. The iZotope Radius TCE engine used in X-Form is one of the best sounding TCE algorithms on the market, offering transparent time stretching and pitch shifting results. Also, X-Form is simpler to use and more effective than Time Shift when selected as the default TCE Trim tool because it has just one main Shift control. Another place that X-Form shines is when processing files using extreme settings for compressing or expanding the original file’s length. The nature of X-Form’s iZotope algorithm with its FFT-based processing enables the algorithm to achieve better results than the traditional “frame overlap” algorithms used in other time stretching products.

‘Both Time Shift and X-Form offer phase coherent processing for processing multi-channel tracks. This is especially useful for stretching a multi-channel track while preserving the original audio file’s surround “image”. While both algorithms do phase coherence processing well, X-Form provides results that collapse the image less—resulting in a processed audio file that more closely resembles the original audio image. The Polyphonic algorithm in X-Form is able to preserve formants on polyphonic material, which is a feature that only Celemony Melodyne could do in the past. X-Form can preserve formants in Monophonic or Polyphonic modes while Time Shift can only preserve formants in Monophonic mode.’

Excerpt from In the Box Music Production: Advanced Tools and Techniques for Pro Tools by Mike Collins © 2014 Taylor & Francis Group. All Rights Reserved.

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