Acid Pro offers enormous power and real-time processing capabilities, which make it an ideal tool for music production. The new version 4 adds a significant number of features, and Acid moves ever closer to an all-in-one media-production environment.

Sonic Foundry's Acid Pro is widely recognized as the premier loop-assembly tool available for the PC today. Although its interface is not as well suited for live performance as, say, Ableton Live's, Acid's enormous power and real-time processing capabilities make it an ideal tool for music production.

The new version of Acid adds a significant number of features, including support for more audio protocols, such as ASIO; 5.1 surround mixing; and the ability to use VST Instruments, under the control of MIDI tracks. With those and several other additions and enhancements, Acid moves ever closer to being an all-in-one media-production environment.

We reviewed Acid version 3.0 in the May 2002 issue of EM, so I'll focus primarily on the new features in version 4.0a and mention existing features only in passing.


Among the major new features of Acid Pro 4.0a is the ability to use VST Instruments in your projects (see Fig. 1). Acid's Soft Synth Chooser will search your hard drive to find all the VST Instrument plug-ins on your system. If you have Instruments scattered among several folders, you can use the VSTi Preferences dialog to identify as many as three locations for Acid to access. You'll also use that dialog to update Acid any time you install a new synth or sampler.

After several attempts, I couldn't get Acid to see all my VST Instruments. Then I tried a tip I found on Sonic Foundry's Web site: I deleted Acid's VST key in the Windows Registry. Everything worked fine on my next attempt.

You can automate Instrument parameters by recording MIDI data directly onto an Acid track (more on MIDI later). In addition, you can add DirectX effects to a synth's output using the same methods you'd use for your audio tracks: adding a Track effect directly to the track, using a DirectX effect with an Assignable effect, or assigning the track to either a sub or the Master bus and applying the effect there — Acid provides lots of flexibility. Building a chain of effects is easy, and once you have a sequence of effects that you like, you can save it for use in other projects.

Speaking of effects, you can now automate the parameters of many effects, including Track EQ, Resonance Filter, and Flange/Wah/Phase. Click on the Track FX icon and select an effect from the Audio Plug-in dialog. Then click on the FX Automation icon, and you'll see the parameters of the plug-in you've chosen. Enable automation for one or more parameters, and when you return to the main Track view, you'll find color-coded envelopes for all the parameters you've enabled. In addition to linear envelope segments, Acid Pro 4.0a supports several new fade types, including fast and slow fades.


Another major new feature in Acid Pro 4.0a is MIDI recording and editing. You can record in either real time or step time, but there are some limitations. For starters, assuming you want to hear what you're recording, you must route your MIDI controller's input to the soft synth you're playing, by using the MIDI Thru drop-down menu in the Record screen. You can't simply enable a MIDI track for recording and assign that track's output to the synth as you would in a dedicated MIDI sequencer. You also don't double-click on an Event (Acid's name for what some other programs call a clip) as you would in a sequencer to access the data once it's recorded. Instead, you have to click on the track's Track Properties icon, then tab to the Piano-Roll Editor. On the other hand, the data you record is stored in a separate file, which makes using it in another program easy.

Editing features are functional but also somewhat limited. You can only edit controller data in the Event List, and the quantization feature is fairly basic. Besides Cut, Copy, and Paste, you can edit individual Events in the Piano Roll or create new Events, but that's about it. However, if you need more complex MIDI data in your Acid projects, you can easily import existing Standard MIDI Files. Moreover, Acid's painting and drawing tools are especially useful for entering MIDI notes.

Because Acid supports Yamaha's OPT (Open Plug-in Technology) format, you can also use third-party MIDI effects plug-ins, such as those made by GenieSys ( Unfortunately, OPT is not the format used by Cakewalk in Sonar and Steinberg in Cubase SX.

Like many other audio programs, Acid Pro 4.0a doesn't let you record the output of a soft instrument as you are playing it. Instead, you must record the MIDI Events that will control the soft synth or sampler, then render the track to a new audio file. The rendering process is much faster than real time, and once it is complete, you can paint or draw Events that play the file directly into the new audio track that will have been created.


Acid Pro's new Surround Panner is a very efficient way to create a surround mix. Choose 5.1 Surround as the Master Bus mode of a new project, and you'll see a small surround-pan icon appear on each new audio track. You can move the track's position in the mix by dragging the icon or by accessing the Surround Panner window (see Fig. 2), which provides a larger surface on which you can create more precise moves.

In the Surround Panner window, you'll find an LFE tab that is used to send the track to the Low Frequency Effects channel. You can assign a low-pass filter (required by some surround authoring systems) to that channel using the Track's Audio Properties. You'll also find a slider to adjust the volume of the center channel, as well as a Smoothness control, which appears if you have keyframes on your track. Keyframes are used to automate a surround track's pan position and are created directly under the audio display in the main track window. Like breakpoints in envelopes, they determine the pan location at a specific point. Acid interpolates the correct values between each pair of keyframes using the same type of fade curves that it offers for stereo panning and volume control. According to the manufacturer, the Smoothness control affects how the sound moves between points on the pan curve. Because I didn't have a multichannel audio card in my review rig (a Pentium 4/2.4 GHz running Windows 98 SE), I couldn't test that feature.

The Surround features are very intuitive and easy to use, though it would be nice if the pan icon moved to reflect the current location of your sound as it plays back. Sonic Foundry has just announced the new 5.1 Surround Plug-In Pack for Acid, an AC3-encoding and DVD-burning utility, which will further enhance Acid's surround capabilities.


Acid Pro 4.0a adds several new features that will appeal to anyone working with animation or video. For starters, you can now preview video using pixels that are either square (used for computer-monitor viewing) or nonsquare (used for TV viewing). You can also encode a video and accompanying audio track into MPEG-1 format for use on a VCD or into MPEG-2 format for use on a DVD. The default encoding presets are fairly basic, but the optional Professional MainConcept MPEG Plug-In ($99) gives you a wide range of options. And, of course, you can preview video on an external monitor if you have the appropriate hardware.

Acid Pro 4.0a offers a number of other enhancements, such as new pan types (equal power and balance), optimization of the Beatmapper's time-stretching and pitch-shifting algorithms, Windows Media file support, and more customization options for default track properties. In the looping arena, you'll find support for alternate time signatures, from 1/1 to 99/32, as well as new options in the Chopper, which make assembling grooves even easier.

Adding major new features such as MIDI recording and editing and surround sound to a mature program such as Acid can result in a bit of a kludge. But Sonic Foundry has done an admirable job of integrating those new resources in a mostly efficient way. If you're already an Acid user, you'll really appreciate the major new tools that version 4.0a gives you. If you haven't yet joined the Acid community, now is a great time to sign up.

Dennis Milleris an associate editor ofEM.

Minimum System Requirements

Acid Pro 4.0a
Pentium II/300; 64 MB RAM; Windows 98 SE/2000/ME/XP


Sonic Foundry
Acid Pro 4.0a (Win)
loop sequencer
direct from Sonic Foundry $399
direct download $349
upgrade from 3.0 $149


PROS: MIDI recording and editing. VST Instrument support. Excellent surround-panning capabilities.

CONS: Only one video track. Limited MIDI editing.


Sonic Foundry, Inc.
tel. (800) 577-6642