Change pitch and tempo with this elegant plug-in. Anyone who works with audio samples knows how important time-stretching and pitch-shifting can be in

Change pitch and tempo with this elegant plug-in.Anyone who works with audio samples knows how important time-stretching and pitch-shifting can be in getting your sounds just right. Nearly every audio editor offers some form of these two DSP algorithms, but they are likely to be fairly basic and have limited effective ranges. To address these tasks more professionally, Wave Mechanics has released Speed, an AudioSuite plug-in that lets you change the pitch, length, and tempo of your audio files. It's one of only a few dedicated programs that offer these features, and it can be just the right tool in many situations.

Speed doesn't require that you have any TDM hardware - all you need is Pro Tools or other software that supports the Digidesign AudioSuite plug-in standard (Emagic's Logic Audio, for example). I tested Speed using Pro Tools 5.01 on a Power Mac 9500 with a 300 MHz Crescendo G3 processor upgrade card loaded with 192 MB of RAM. Among the plug-in's several user interfaces is the Simple control panel, which makes working with Speed nearly automatic. You can also switch the display to the Calculator or Graphical screen (more on those features later).

SPEED ZONETo use the plug-in, first select an audio range in the Pro Tools Edit window, then choose Speed from the AudioSuite menu. The default control panel, Simple, will appear. The Preview button at the bottom of the window lets you audition the current tempo and pitch settings (the default settings signify no change to your audio). Clicking on the Process button initiates DSP processing of your selected audio and saves the results to disk.

You use the Speed Control knob (on the left) to change tempo without altering pitch, and the Pitch Control knob (on the right) to change pitch without altering tempo. You can also click on the displayed value and type in a new setting. Both Speed Control and Pitch Control have different modes, which you select by clicking on the small white triangular Mode Select tabs in the middle of the window.

Speed Control has two modes: Tempo and Length. A Tempo setting above 100 percent increases the tempo, and a setting below 100 percent reduces the tempo. For example, a Tempo setting of 200 percent will result in a tempo twice as fast as the original, and a setting of 50 percent will give you a tempo half as fast. (Settings for Tempo and Length range from 50 to 200 percent, with a resolution of six decimal places in Simple and Calculator mode and three decimal places in Graphical mode.) In Length mode, higher settings lengthen a selection, resulting in a slower tempo, and lower settings shorten the selection, creating a faster tempo. As with Tempo mode, a 100 percent Length setting has no effect on the audio.

Pitch Control has three modes: Cents, Semitones, and Percent. Both Cents and Semitones let you shift your audio a maximum of one octave in either direction. Percent mode uses a frequency ratio to define the change; a value of 100 percent, for example, won't modify the pitch. (Settings range from 50 to 200 percent.) This mode resembles the pitch-ratio control of older hardware pitch-change devices and can compensate for the pitch change produced by sample-rate conversion.

BY THE NUMBERSLike the Simple screen, Speed's Calculator control panel offers speed and pitch controls: Pitch Calculator and Speed Calculator. Each has two modes. Pitch Calculator's Key mode transposes music between specific keys, and Tuning mode converts audio from one tuning reference to another (for example, A 440 to A 438). Just enter the original key or tuning reference in the Original field and the desired key or tuning reference in the Modified field.

Speed Calculator offers Tempo and Length modes. In Tempo mode, type a new bpm value in the Modified field; then click on the Preview button to audition the altered tempo and hit Process to make the change. Length mode lets you stretch or squeeze your samples by specifying a new length measured in either samples or seconds.

Length mode also gives you access to the Length Copy feature, which is displayed on the screen as a curved arrow. You can use Length Copy to make several audio regions identical in length - a useful tool when working with drum loops. First select the region with the desired length, then click on the Length Copy arrow. The selected region's length will appear in the Modified Length field. Next select the region whose length you want to change. The Original Length field will show the region's length, and the Percentage Change field will indicate the difference between it and the desired length. Click on the Process button to make the change.

BEND AND STRETCHSpeed's secret weapon is the Graphical control panel, which offers an easy way to insert pitch and timing changes at any point in your audio file. It's also handy for creating accelerandos and decelerandos. This screen displays a visual representation of the audio waveform, overlaid with two horizontal "graph" lines. The white line controls tempo/speed, and the blue line controls pitch. (Both are initially set to have no effect.) Clicking on the Mode Select tabs calls up multiple display options, much as they do in the other modes.

Editing in the Graphical window is very similar to editing automation data in Pro Tools. Click on an existing point (shown as a tiny square) and drag it to a different location to adjust pitch or timing. To create a new point, click on the display at the desired location. You can delete any point (except the start and end points) by Option-clicking on it. If one line obscures the other, Control-click to bring the hidden line to the front. Be careful not to drag a point to a new value or insert a new point when you Control-click on the line. The process works fine with a little practice.

Shift-clicking or Command-clicking on a point will constrain it to vertical or horizontal movement, respectively. Whenever you select or move a point, its speed- or pitch-change value is shown beneath the waveform display, along with its time position (in either seconds or samples). You can also type specific pitch and time values directly into the fields.

IN ACTIONSpeed is not the tool to use for vocals: changing a sample's pitch moves the formants as well as the rest of the sound (although that's not the case with tempo). Formants are the characteristic resonances of a human voice or musical instrument. Formant frequencies remain constant regardless of which pitch you sing in or what note you play on your guitar. Ideally, moving the formants would be optional, but Speed always moves them when it's processing the pitch. Also, increasing or decreasing an audio file's tempo speeds up or slows down any vibrato in a telltale way, a problem that no time-compression software has solved.

I recorded acoustic guitar arpeggios from the bottom F upward. When I moved the pitch down by one semitone from F to E, the sound was perfect. When I moved it to E-flat, however, the instrument did not sound completely natural, though it might have fooled some listeners. The imperfection became more noticeable when I lowered the pitch to D; and at D-flat the sound was too unnatural to use - the timbre took on an uncharacteristic buzz, although there were no sound glitches. When I raised the pitch four semitones, the guitar sounded as though I were using a capo, but transposing five or more semi-tones produced an unnatural sound.

I also used my acoustic guitar to compare Speed's time-stretching capabilities with those of the standard Pro Tools AudioSuite plug-in. Speed introduced minimal artifacts into the processed sound over the entire 50 to 200 percent range, and I preferred its sound to that of the Pro Tools equivalent.

Next I recorded a drum pattern consisting of bass drum, snare, hi-hats, and congas. The groove sounded perfect all the way from 50 to 200 percent of the original tempo. To test the pitch-shifting, I highlighted two bars of drums and clicked on Preview, and as the sound looped I moved the Pitch Control knob. Again, the drums sounded unnatural if I shifted them more than a few semitones down or 3 or 4 semitones up. However, the unnatural quality produced by extreme stretching or shifting could suit your purposes. I time-stretched the same audio selection with both Speed and the standard Pro Tools time-stretching plug-in. Speed definitely won out - barely any audible artifacts were introduced into the sound.

SIMPLICITY ITSELFSpeed's documentation is brief but adequate - after all, this is not a very complex piece of software. The manual mentions a couple of applications (such as shortening a 35-second commercial to 30 seconds), but a few more examples would have been beneficial. Wave Mechanics' Web site offers little more than the manual, although its up-to-date problem list may prove helpful. The software's copy-protection scheme requires a key disk, so you'll need to keep a floppy on hand. Speed's Simple control panel couldn't be more intuitive, which is exactly what you need for a busy Pro Tools session. The Calculator screen is very useful when you know what settings you need, and the brilliant Graphical window lets you apply detailed changes to different parts of your audio.

Speed is ideal for trying out ideas in Pro Tools with any kind of audio material. I appreciate Speed's capabilities more with each use. I wouldn't run a Pro Tools session without it.