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Sonic Foundry Acid Pro v3

PC Audio Loop Sequencer
Published January 2002
By John Walden

Sonic Foundry Acid Pro v3 main screen.Acid Pro v3 main screen.

Sonic Foundry were the pioneers of loop‑based PC sequencing with the initial release of Acid. More than three years on it's more popular than ever, and the latest version includes MIDI and video support among other new features.

Whatever your views on the 'paint by numbers' approach to music creation offered by loop‑based audio sequencing, there is no doubting its popularity. Armed with the right software and a few suitable loops, even a musical novice can produce creditable results. Sonic Foundry's Acid has been at the forefront of this mini‑revolution, and when Martin Walker reviewed the first version in November 1998, there was little in the way of competition. Three years down the line, a number of other products are now available. These include Cakewalk's Club Tracks and, more recently, Sonar (although this is also a fully featured MIDI and audio sequencer), Making Waves (reviewed in SOS December 2000), eJay's Dance and Techno software, and Bitheadz's Phrazer for the Mac (SOS April 2001). Sonic Foundry have also been busy during this time, and a number of cut‑down versions of Acid have appeared, each bundled with a themed collection of loops and at a price that almost anyone could afford.

The flagship Acid Pro has now reached version 3 and, along with the usual collection of tweaks to the user interface, the new release also includes a number of major additions. The two most obvious new features are MIDI tracks and a Video window, but there are also two new tools: the Beatmapper and the Chopper. Are they enough to keep Acid ahead of the competition?

Bundled Joy

The boxed version of Acid Pro contains considerably more than just Acid. Also included are cut‑down versions of other Sonic Foundry software in the shape of Sound Forge XP Studio and Vegas Audio LE. Sound Forge XP provides a competent audio editor, including tools to edit loops for use with Acid, while Vegas Audio LE is a basic eight‑track audio sequencer. In addition, Sonic Foundry's XFX1, XFX2 and XFX3 effects packs are included, providing 18 DirectX audio plug‑ins such as chorus, delay, distortion and reverb. Finally, a collection of some 600 loops is supplied covering styles including dance, techno, pop and rock.

Of course, the key element in the bundle is Acid itself and for those new to loop‑based sequencing, a brief introduction might be useful. Essentially, Acid provides a means of sequencing short audio files along a timeline in a fashion no different from the 'arrange' window of most MIDI or audio sequencers. However, the fun starts when Acid knows the tempo (the loop's length in beats) and pitch (the root note of the musical phrase) of the audio involved, as the software can then adjust both the pitch and tempo of the audio in real time. For example, a drum loop recorded at 120bpm can be automatically time‑stretched to play back at 100bpm while maintaining the original pitch, or a bass line recorded with a root note of A can be pitch‑shifted to play back with a root of G but without altering its tempo.

For loops you create yourself, Acid will do its best to estimate the tempo. If the user specifies the root note, then the software's pitch‑shifting algorithm will also be able to go to work. Both this pitch and tempo information can also be fine‑tuned using Sound Forge XP if required. As described more fully below, the end result is a system that allows quite complex arrangements of audio loops to be constructed, all with the flexibility of instant pitch or tempo adjustment.

Getting Started

Obviously, you need a soundcard and CD‑ROM drive to use and install Acid: as far as PC specifications go, Windows 98, Me and 2000 are all suitable, and Sonic Foundry suggest a modest 300MHz processor with at least 64Mb of RAM and 60Mb of free hard disk space. A 400MHz processor and Windows 98 SE, Me or 2000 are the minimum specification for those wishing to use the video playback options.

On the test system, installation took just a few minutes and proceeded without any problems. When first run, Acid Pro defaults to using the sound device currently selected by Windows and detects the presence of any otherDirectX plug‑ins present on the system. Sonic Foundry have recently improved their registration process and, with a suitable Internet connection, it took just a few seconds to fully register the software.

Track Properties for timestretching a loop.Track Properties for timestretching a loop.

While Acid has undergone both some cosmetic and functional changes in its user interface, the main screen looks pretty much as it always has in its fundamental respects. The display is divided into four main areas. The Track View dominates the top right and provides the traditional timeline view through the project. Immediately to the left is the Track List which, as well as indicating the file name of the audio file associated with each track, also provides access to various mixer functions such as volume, pan, mute, effects send levels and output assignment. The left‑hand side of the bottom half of the screen serves a number of functions, with a series of tabs allowing the user to toggle between these views. Probably the most important of these are the Explorer, for finding and auditioning audio files, and the Track Properties view where, among other details, the root note and length of a file can be specified. To the right is a more traditional mixer view. The number of channels available here depends upon how many busses or effects channels the user has defined. All of these four main screen areas can be resized and many of the windows can be docked into the bottom half of the screen if preferred.

Library Work

While creation of your own loops is a simple process using Acid and Sound Forge XP, Sonic Foundry have an extensive range of loop CDs available and it is well worthwhile budgeting for a few of these to get yourself started. The ground covered by the existing libraries is very diverse. As might be expected, there are plenty of drum loop libraries but the styles go from straight rock, through Latin, dance, hip‑hop and into world beats. The music loop libraries cover the same territory but also include blues, country, various ambient collections, jazz and orchestral styles.

As well as regular new releases, Sonic Foundry now also offer some themed 'packs' such as the Drum Pack, Producer Pack or Dance Pack. Each Pack comprises a collection of four or five loop libraries fitting the named style but at a discounted price. More details on the loop libraries, plus some example loops from each, can be found on Sonic Foundry's web site.

Going Loopy

The basic process of song construction in Acid is simple. Acid automatically creates a new track for each media file added to the project, and 'Events' (instances along the timeline when the file is playing within the arrangement) can only be placed on that track. To insert such Events, a pencil tool can simply be pointed and dragged in the appropriate place on the Track View window. The Track View includes vertical and horizontal zoom buttons, situated in the lower right corner of the scroll bars for the window, and the zoom level affects the resolution of the grid displayed in the timeline to which Events will snap. Snapping can switched off, enabled for just the grid lines or enabled for other location points such as the cursor position or markers, so getting an Event exactly where you want it is a breeze.

Three types of track are available: Loop, One‑Shot and Beatmapped. Loop tracks are the most commonly used and are usually based on fairly short audio sections that are designed to contain a discrete musical phrase. These files are held in RAM once added to the project. Drum loops, bass riffs, short melody lines or chord sequences would be obvious examples. Loops can be set to follow the tempo and/or key changes as required via the Track Properties tab in the bottom half of the screen.

Both tempo changes and key changes can be inserted at any point along the timeline. Any Loop tracks that have been set to follow such changes will then do so in real time. As with any tempo‑ or pitch‑shifting process, audio artefacts will become apparent if it is pushed to extremes, but modest shifts of up to a few semitones in pitch or tempo changes of 10‑15 bpm work remarkably well. Via the Explorer, new loops can be auditioned in real time with the current project playing — Acid will automatically pitch‑ and time‑shift the loop being auditioned to fit the project. It is this core feature of Acid that makes it so easy to construct a complete song with just a few well‑chosen loops, and if you don't wish to roll your own, Sonic Foundry have an extensive collection of loop library CDs available (see the Library Work box for more details).

One‑Shot tracks are based on short sections of audio that are not designed to be looped. If longer than a few seconds, they are usually streamed from hard disk rather than held in RAM. One‑Shot tracks will not change pitch or tempo with the rest of the project. Cymbal crashes or sound effects might fall into this category.

Beatmapped tracks replace the Disk‑Based tracks of previous versions. These tracks are based on longer audio sections and, by default, when a file longer than 30 seconds is added to a project, the Beatmapper Wizard is automatically opened. This Wizard allows the down beats and tempo of the file to be identified. Both can be adjusted and auditioned by the user until they are spot‑on. This tempo information can then be added to the file, allowing it to be time‑stretched or compressed to match the project tempo. This tool does take a little getting used to but is an extremely useful addition to Acid.

SONIC FOUNDRY ACID PRO V3The simple use of this tool would be for adding longer drum loops to a project, but two other obvious applications spring to mind. First, longer vocal sections such as a complete verse or chorus might be subjected to the Beatmapper treatment. The tempo of the vocal could then be automatically adjusted if you need to adjust the overall tempo of the project. Second, whole tracks could be imported (for example, using Acid's new CD ripping facility), Beatmapped, and then have their tempo adjusted. If you wanted to compile an extended dance mix based upon a number of songs, get them all running at the same tempo and add some additional drum loops, the Beatmapper would make this very straightforward. The Beatmapper is not so effective if the file being mapped is not at a constant tempo, but otherwise works very well.

Allied to the Beatmapper is another new tool, the Chopper (no smirking at the back!). Selecting any event and then clicking the Chopper tab brings up an alternative waveform view in the bottom portion of the Acid display. In this view, sections of the overall file can be selected and auditioned. Selected sections can then be added to the Track View as a new track, and Events based upon this selection drawn into the arrangement. This was possible in previous versions of Acid, but the Chopper certainly makes this task easier. Using this tool to isolate particular musical phrases from a lead guitar solo or to extract an individual bass‑drum beat from longer audio files is very simple. While these functions could easily be achieved within a standard audio editor, it's useful to be able to do this quickly and efficiently from within Acid. It would also be possible to use this tool on completed tracks, so cutting up and rearranging a finished tune while making tweaks to its tempo and adding extra rhythm parts could all be attempted from within Acid.

Bundled Effects

The three XFX packs bundled with Acid Pro provide a good range of DirectX plug‑ins. These include:

  • Reverb.
  • Compression.
  • Pitch‑shift.
  • Chorus.
  • Delay/echo.
  • Noise gate.
  • Multi‑band dynamics.
  • Graphic dynamics.
  • Parametric EQ.
  • Paragraphic EQ.
  • Graphic EQ.
  • Amplitude modulation.
  • Flange/wah‑wah.
  • Smooth/enhance.
  • Gapper/snipper.
  • Vibrato.
  • Distortion.

On The Record

Acid can, of course, be used to record new audio tracks. However, unlike previous versions, recording now includes MIDI as well as audio. Clicking on the Record button in the Transport area brings up a dialogue: for audio tracks, the input source, sample rate, bit depth, recording folder and file name can all be specified. When the recording is stopped, the recorded audio is placed upon a new track within the Track View — all very fuss‑free.

MIDI recording is also a straightforward process. MIDI in and out options can be specified via the Preferences settings from the Options menu. Once this is done, MIDI tracks can then be recorded and again, once the recording is stopped, the MIDI data appears as a new track in the Track View window. Copies of MIDI sequences can be drawn onto the Track View window in the same way as audio loops and, via the Track Properties tab, basic MIDI properties such as channel, voice, volume and pan can be set. However, in terms of MIDI functionality, that is more or less it: any editing would require an external MIDI editor. While it is an interesting development to see any MIDI sequencing functionality in Acid, it is a shame that it does not as yet provide something like a piano‑roll editor to allow even some basic tweaking of MIDI data.

This said, Acid's synchronisation capabilities via MIDI timecode or MIDI clock mean that it can easily be used in conjunction with a MIDI + Audio sequencer. As a regular user of Acid Pro, I've found that hooking it up with my sequencer of choice (Emagic's Logic) has usually been a pretty painless experience.

All Mixed Up

With each audio loop requiring a separate track in the Track View, it is very easy to end up with an awful lot of audio tracks that need mixing. Acid provides a good range of possibilities in this respect. Individual tracks can, of course, have their individual levels, pan and effects chains specified via the Track List. However, the Mixer tab provides access to a range of other possibilities. By default the Mixer window shows two faders, Master and Preview. The former controls the overall output while the latter controls the volume level at which new loops are auditioned via the Explorer. If the host PC has multiple audio output options available, the destination of each fader can be specified.

New fader objects can be added in the form of busses and assignable effects controls. Up to 26 busses can be added to a project and individual tracks from the Track List can then be assigned to a particular buss. For example, all the drum tracks in a song might be assigned to a stereo buss. The faders on the Track List can then be used to control the levels of individual drum parts whereas the buss fader can be used to control the overall level of the drums relative to other elements in the mix. As with the master fader, busses can be routed to any of the PC's available audio outputs. Busses can also have effects added to them if required.

While effects (or chains of effects) can be added to both individual tracks and busses, in terms of processor overhead it is clearly sensible to have some global effects or effects chains to which signals from any track or buss can be passed. Acid calls these assignable effects, and up to 32 fader objects of this type can be used. The most obvious application of these would be a general reverb or delay treatment, but effects can be chained if required. Send levels can be set for individual tracks in the Track List or from busses.

The DirectX effects supplied with Acid cover all the main bases (see the Effects Box for a full list) and the quality of the processing is of a high standard with plenty of control on offer. The more routine processes such as delay, chorus, compression, flange, and so on offer exactly what you would expect, and the reverb quality is good. The plug‑ins include a multi‑band dynamics option, which offers four bands of compression. This could have a number of applications, and applied across the master output can add considerable punch to a final mix.

Like most modern audio or MIDI applications, Acid provides facilities for drawing envelopes upon tracks or events as a means of mix automation. The envelope tool can be used to draw levels for volume, pan and effects sends: these are followed in real time during playback.

In The Frame

The Video window is a new feature in version 3. A single video file can be opened within a project, with both Quicktime (MOV) and Video for Windows (AVI) file formats supported. As well as playback in the Video window, a frame strip is inserted as the first track in the Track View window. Any audio included within the video clip is automatically inserted as a One‑Shot track.

Using loops to build a musical bed for video footage is a sort of halfway house between using library music selections and composing something from scratch. With a suitable collection of loop CDs, the process can be very efficient, flexible and a whole lot of fun. Tempo changes can, of course, be inserted at key scene changes in the video so that the pace of the music can change to reflect the visual action. Acid also provides some tools for automatically calculating the required tempo for a section of the project so that the music will hit specific points in the video playback, thus offering more control over tempo and cue length than would be available when working with library music selections.

Finished Product

Once a project is completed, a range of output options are available. Stereo mixes can be created and, via the Render As option from the File menu, all the essential file formats are supported. These include MP3 audio with an excellent range of options in terms of data compression levels. If you're working with a video clip, Acid also offers options to render AVI, MOV or Windows Media Video (WMV) files that combine the original video footage with the Acid‑generated audio. As with straight audio output, options are provided for compressing the video file, with options to reduce frame size and rate as well as settings designed for the creation of streaming media — all very useful for video to be delivered via the Internet.

Conclusions

Sonic Foundry have made some significant additions to Acid in this release. While its core function remains the mixing and matching of loops via its excellent tempo‑ and pitch‑matching capabilities, with the Beatmapper, Chopper and Video window, they have widened the software's appeal to those interested in remixing and producing music for picture. The addition of MIDI tracks is welcome even if the lack of MIDI editing is a restriction.

Of course, there is competition out there, most notably Cakewalk's Sonar which offers a sophisticated MIDI + Audio sequencer as well as Acid‑like tempo/pitch‑matching functionality. However, if you are not an existing Cakewalk user, sync'ing Acid to your sequencer of choice does provide a fabulous combination of creative tools.

At this price, Acid Pro will not be a casual purchase for most people. It is, however, a thoroughly professional product and capable of some wonderful results. If you just want to experiment with a few loops, then one of Acid's cut‑down siblings would make a good starting point. Be warned, though: Acid is an addictive substance and many people experimenting with the starter versions will soon find themselves craving a bigger fix. As serious software goes, Acid Pro v3 is an awful lot of fun!

Published January 2002