Sonic Foundry Acid Pro 3.0 Review

When Acid was introduced, it was hailed as a breakthrough product, and rightly so. The program simplified the process of creating music using sample loops

When Acid was introduced, it was hailed as a breakthrough product, and rightly so. The program simplified the process of creating music using sample loops by enabling audio files with contrasting tempos and pitches to play together in time and in key. Gone was the tedious pre-production process of recalculating loop lengths and pitch changes that was necessary before assembling loops into a song. Acid calculated those changes on the fly and in real time.

Since then other companies have introduced programs that let you create music by sequencing sample loops with different pitches and tempos. Some of them are quite good, and some are merely adequate, but none does exactly what the latest version of Acid does.


Acid allows you to arrange audio loops and hits through a simple drag-and-drop interface (see the November 1998 issue for a review of Acid version 1.0). It doesn't matter what the sample's original tempo or pitch is; Acid automatically stretches and transposes it to fit the current project's tempo and key. Like the original version's, Acid Pro 3.0's interface is divided into three main sections: the Track List, the Track View, and the multifunction Accessory panel (see Fig. 1).

When you first open the program, the Track List and Track View areas are empty, and the Tempo and Tuning parameters are set to default values of 120 bpm and the key of A, respectively. The lower part of the screen displays the Explorer, where you view and preview the various files that can be used in Acid. In addition to 16- and 24-bit WAV and AIFF files at sampling rates as high as 192 kHz, Acid Pro 3.0 now supports other audio file formats, such as MP3, Ogg Vorbis, and Windows Media (export only). Just click on any file, and Acid will preview it at the tempo and key specified in the bpm and Tuning settings.

Acid Pro 3.0 has independent transport controls in the Explorer area that let you control preview playback independent of the main transport. You can also route preview material to a separate audio bus if you have a multichannel audio card (see Fig. 2). That allows you to control the preview volume independent of the main mix, which can be an ear saver if you happen to select a particularly loud loop to preview.

Once you pick a loop or other audio file, drag it to the Track List or Track View area to create a new track. (Each file is assigned a separate track.) Tracks contain Events that indicate how and when the assigned file should be played. Acid typically loads short audio files into RAM, which improves performance in playback. (Users can set a duration threshold above which files are streamed from disk.) A numeric indicator in the lower-right corner of the screen indicates how much memory is used for samples compared to overall system memory. When a file is longer than the user-defined limit, the Beatmapper wizard goes to work. Beatmapper lets you add tempo information to a file, making stretching the file easier.

Once you've created a new track, you tell Acid where in time you want the file to play. Using the Draw tool, left-click and drag the mouse to insert Events into a track. To edit an Event, simply grab its end point and drag it to the right to expand or left to contract it. You can also click on an Event to highlight it and then move it to a different start point in the timeline. However, you can be more selective about what to play in a track, as you'll see shortly.

Although Acid works with sample data, you can improve performance if you first Acidize the file. That can be done directly in Acid, Sound Forge 5, or Sound Forge XP 5.0, which comes in the bundle. That process adds an extra chunk of data to the file's header that contains settings specific to Acid, including the type of sample, its number of beats, its root note for transposing, and its stretching properties. You can also specify whether the file should be looped, played as a one-shot, or beat-mapped and whether it should include beat info and a base note for transposition, assuming you want the file to be transposed. Drum loops, for example, don't usually contain a base note, because you don't want the pitch to change whenever the tempo changes.


The first time you import any given large audio file into Acid, the Beatmapper wizard starts if the program does not detect any tempo information in the file. Run the wizard, and Beatmapper synchronizes the file's tempo to the tempo of the current project. If you select No, the file maintains its original length regardless of your project's tempo.

Beatmapper works by identifying the downbeat of the first full measure and placing a marker at that point (any pickup beats before the first full measure are ignored). Then, it estimates the length of the measure and highlights a region in the file's waveform display to indicate where the first measure is. You can move the marker for the first downbeat to the correct position if it's incorrect or adjust the size of the region if needed.

The final step is to ensure that each measure in the file has been marked off properly by the Beatmapper. As far as I'm concerned, that's a useless exercise, because most long audio files rarely play back perfectly in time from beginning to end — the measure markers are going to be off after a while. However, as long as the downbeat for the first measure is in the right place and you have the true length of the first measure, the Beatmapper keeps the remainder of the track in tempo pretty well.

When Beatmapper finishes, you can change the project tempo to match that of the beat-mapped track. You can also preserve the pitch of the beat-mapped track if the project tempo changes. Beatmapper information is saved with the file so that you won't have to run it again the next time you use that file.


As mentioned earlier, you aren't limited to playing complete loops in a track. Acid Pro 3.0 now includes the Chopper tool, which makes it simple to dissect, isolate, and insert parts of loops into tracks. Open the Chopper tool from the View menu or select the Chopper tab in the lower-left corner of the screen (see Fig. 3). Then, click on the Track List or Track View to select a loop, and its waveform display appears in the Chopper window. Now, highlight an area — a snare hit, for example — and play it using the Chopper's transport controls. Once you have captured the correct loop segment, use the Insert button to place it into the track at the cursor point as many times as you want. (There's no way to insert the segment multiple times automatically.)

If you activate the Link Arrow to Selection button and drag the arrow forward or backward, you can add space around your loop segment to create interesting stuttering effects or gaps in the audio track. You'll also find numerous tools in the Chopper that make moving a region or modifying its length simple. For example, it takes only one click to double or halve the size of the highlighted region or to shift it left or right. Best of all, you can use musical durations to define the size of a region; values from full measure to 32nd-note triplet are available. A custom setting accepts fractional durations larger than one measure (for example, 1.01 or 1.25 measures).


One of the most useful new editing features is Ripple Editing, which closes up gaps when you cut or delete highlighted sections of track data. Ripple Editing also lets you paste data into a track and move existing data back to make room for the new data. That is an excellent tool for rearranging entire sections of a song. Acid also has a new fade-in/fade-out function that makes it easier to create track fades. Just move the Draw tool to the upper corner of a track, and a little Fade icon appears. Drag the Fade icon to the desired point, and you get a perfect fade-in or fade-out. If you right-click on the Fade icon, a drop-down box showing linear, fast, and slow fade shapes appears. Choose the type of fade you want, and it appears on the track.

Acid Pro 3.0 includes all three of Sonic Foundry's XFX DirectX audio effects plug-ins (18 total), which are also sold separately. Furthermore, you can now use effects as track inserts (Track Effects), through an effects send/return bus (Bus FX), or on an effects chain (Assignable FX). You can have as many as 32 effects per track, 26 buses, and 32 effects chains.

Acid Pro 3.0 has the ability to import an AVI or MOV video file into a project; that allows you to create loop-based tracks that are synced to video. Being able to see your video on a frame-by-frame basis makes that an especially useful feature. You can also add a graphic image in one of several common file types (TGA, BMP, PNG, and so on) for use as a background image.

Acid Pro can now record and play back multichannel MIDI data on one or more tracks. (Acid recognizes MID, SMF, and RMI MIDI file types.) There isn't much MIDI editing capability available — you can alter the tempo or shift the pitch of an entire Event up or down in semitone increments — but it's a handy feature nonetheless. You can link directly to a sequencer (if you've specified one in the Preferences menu) and load DLS files for Acid to use when playing MIDI data. If you don't have a DLS-compatible sound card, Acid can use the DirectX soft synth for playback.

You will have no trouble finding files for use in your music. There are dozens of CDs in the Sonic Foundry Loops for Acid collection, and you can rip (or burn) CDs directly from within the program.


Although Acid continues to get better and better, you still can't mute, unmute, and solo tracks on the fly using the computer keyboard. That would let you audition groups of tracks without having to assign them to a particular bus beforehand, and it would be helpful when using Acid in live performance. I'd also like the ability to control Acid with MIDI data coming from a sequencer or an external controller.

I have no other complaints about Acid Pro 3.0. I like the improvements in the program's functionality and the value added by the inclusion of Sound Forge XP 5.0 and all three XFX DirectX plug-in packages. The CD-ROM also contains Vegas Audio LE to whet your appetite for the Vegas Video program.

For those who disdain creating music using loop-based material, I advise you to give Acid Pro 3.0 a close look. I felt that way until I got my hands on the program. Now it's one of my favorite music-making tools. Although it's simple to use, it's no less challenging to create musical pieces with Acid than with other production methods. Besides, the program is just plain fun, no matter what style of music you create — and isn't having fun with music what it's all about?

Zack Priceis a digital-audio editor and a Windows digital-audio consultant in the Chicago area.

Minimum System Requirements

Acid Pro

Pentium II/300 (Pentium II/400 for video scoring); 64 MB RAM; Windows 98SE/ME/2000/XP; DirectX 8.0; 16-bit sound card


Sonic Foundry
Acid Pro 3.0 (Win)
loop sequencer


PROS: Easy to create loop-based songs. Support for MIDI and video formats. Direct CD burning.

CONS: No muting, unmuting, or soloing tracks from computer keyboard. No way to use MIDI to control program. Only one loop per track.


Sonic Foundry
tel. (800) 577-6642 or (608) 204-7680