Interactivity, March 1997 - issue #21

On this page you will find a reprint (by permission from Miller Freeman) of part of an an article by the leading multimedia magazine Interactivity, from the March 1997 issue (#21).

This definitive and in depth roundup of batch audio file processors reviews Audio Ease BarbaBatch, Waves Waveconvert, Airworks S-Link , and Macromedia SoundEdit with Automator.

BarbaBatch clearly comes out on top, offering "...excellent speed, quality, features and ease of use...".

The first three pages (not included) are on stereo editors, the reprinted part of the article is about batch format and DSP processors and has not been edited. We have, however, highlighted sections of special interest in the margins.

In the article some criticism concerning BarbaBatch is outdated since the author of the article was working with a pre-release. Therefore please note that:

1. The current shipping version 2.3 does incorporate a batch file playing section that auditions 13 file formats and includes options for varispeed and separator sounds between auditioned files.
2. The displayed picture of the BarbaBatch interface is outdated, it is, for instance, not showing the dynamics section incorporated in the current shipping version.
3. About everything in BarbaBatch is scriptable.
4. Three file formats that BarbaBatch handles are not mentioned: Microsoft ADPCM, AIFC and System 7 Sounds (soundresource) bring the number of supported formats to a total of 14.
   

(We have sometimes included an Audio Ease note and we have made sections that are relevant to BarbaBatch bold.)

By Atau Tanaka
Format Conversion

Having verified and renamed the individual files, You're ready to convert them to the format in which they'll be delivered, typically a lower resolution format such as mono, 8 bit, 22.05 kHz. Processing hundreds or even thousands of audio files manually isn't the way to spend your weekends - Batch processing is the only way to go. But don't get snookered by the convenience into neglecting quality control. Audio treatments can have different results depending on the source material, and it's frequently necessary to tweak a converted file to compensate. In any case, after automated format conversion or any batch audio processing listen carefully to every file before pressing a CD-ROM gold master or uploading to your web site. Let's take a look at three commercial batch format conversion programs - Audio Ease BarbaBatch ($495), Airworks S/Link 2.1 ($199), and Waves Waveconvert ($300, see review June `96) - and a batch utility called SoundEdit Automator that's included with SoundEdit 16. In S/Link (fig.7) and Waveconvert (fig.8) you can listen to the original file before you convert it and to the result afterward. Waveconvert adds a preview function that converts a short segment so you can test the effect of various settings before you apply them. BarbaBatch (fig.9) and Automator have no facilities for auditioning. (note from Audio Ease:The reviewer was working with a pre-release.In fact BarbaBatch 2.0 incorporates a batch auditioning tool that plays all 14 formats with adjustable speed and separator sounds) . All four programs employ a three-step process:specify input files, specify conversion, and select output destination. To select files for conversion, S/Link uses a Finder like hierarchical file structure that's quite intuitive. Waveconvert, BarbaBatch and Automator use an input file list; the latter two programs let you drag and drop items into the list.

BarbaBatch and S/Link retain the folder hierarchy of source files, while Waveconvert and Automator make you open and empty folders manually into the list, which has no hierarchical structure. This is an important point. Assuming you've organised the source files into folders only BarbaBatch and S/Link can operate without disrupting the structure you've created - which may be critical if you're dealing with, say, a thousand files. Additionally, BarbaBatch can copy and extract regions within a file. That is, if you're working on your master file in Digidesign Sound Designer II, Macromedia Deck II, or another program that supports region definitions and you select `Export Session Regions' BarbaBatch can read the region definitions and extracts the segments automatically.

S/Link is the most basic of the bunch. When you drag folders and files from one window to another , a dialog box appears asking you to specify the output file format, data compression, sample rate and sample size. If you convert one file at a time, you can name the output file and select a region to convert via a simple waveform display. S/Link 2.1 supports the following file formats:AIFF, AIFC, Akai Sampler, AU Sun Next µ-law), CD-Audio, DAWN, Fostex Foundation, IFF/8SVX (Amiga), Lightworks, Mod, Mac SND I and SND II, OMF, QuickTime for Windows, QuickTime including IMA 4:1 compression, Sonic AIFF, SND (Sun/NeXT linear), Digidesign SDI and SDII, SoundEdit and SoundCap, Synclavier/PostPro, WAV (Windows). BarbaBatch has a conversion window- a list of various conversion macros - through which you can check boxes to set conversion parameters, which can be named and saved for reloading later. Since you can check boxes for more than one output format, you can convert each file into several destination formats in a single operation.

BarbaBatch handles the following file formats:AIFF, AU (Sun Next µ-law), AVR, Digidesign SDI and SDII, IFF/8SVX (Amiga), QuickTime, SND (Sun/NeXT linear), VOC, VOC 16-bit, WAV (Windows). (Note from Audio Ease: The reviewer was working with a pre- release the actual shipping version 2.0 adds Microsoft ADPCM, AIFC and System 7 Soundfiles (sound resource). In Waveconvert, you move files from an input list to an output list where you specify the destination format, sample rate, bit depth and data compression. In addition, there are options to apply brightness and dither. The Mac version of WaveConvert handles AIFF, SDII, SND and WAV files.

BarbaBatch and WaveConvert (and its higher end cousin, the L1 Ultramaximizer Plug-In) offer dynamics processing options as part of the conversion process, including noise gating, normalisation, and maximisation. These features are essential for squeezing maximum fidelity out of low bit depths. With a noise gate enabled, any portion of the input signal that falls below a user specified level for longer than a specified time will be silenced. This is particularly for eliminating ambient noise between phrases of speech. BarbaBatch has an adjustable noise gate. WaveConvert offers a choice between two gates, called hard and soft, with fast and slow response times. In addition WaveConvert has a rumble filter for removing DC-offset (which shifts an entire waveform above or below the horizontal zero-amplitude axis) and low-frequency rumble, These components may be imperceptible in a 16 bit file but can cause problems when they're converted to 8-bit. Normalisation boosts the overall level of the file in such a way that the loudest peaks constitute 100 % of the level available. To maximise the file is then limited which reduces the level of peaks only, and boosted so that, once again, the highest peak reaches 100 percent. These steps optimise the file's volume level characteristics for maximum impact within the dynamic range constraints of low-res audio formats.

Once you launch a batch process, the main issues are how long it takes and what kind of status report the software creates. BarbaBatch and Automator create a session log, a text file that reports how many files were converted and whether any errors were encountered. Especially with large batch jobs, the information can be invaluable. The other programs offer no reporting whatsoever. Performance can be ranked in terms of speed and quality. To test the programs we're discussing, I ran them on a Powermac 7100/80 and processed a mixture of SDII files and AIFF files at 16 bit, 44.i kHz resolution. There were 33 files in all, totalling 21 MB or four minutes of audio. To convert this material in a single batch operation to 8 bit, 22.050 kHz AIFF took (in minutes and seconds) S/Link 2:17, BarbaBatch 2:25, WaveConvert 7:12, and Automator 9:00. Adding a maximise to the batch process, BarbaBatch took 4:26 and WaveConvert 7:12. As for output sound quality, all these programs are equally prone to noise during quiet musical passages - the only way to beat 8 bit quantisation noise is to include a maximisation step, either during the batch conversion with BarbaBatch or WaveConvert or applying Waves L1 as a separate step. The results differ most in the high frequencies. S/Link gives the brightest results, followed by BarbaBatch, followed very closely by WaveConvert, then finally Automator. (Bear in mind that Automator's sound is, in fact, that of SoundEdit 16.) Unfortunately S/Link's output is prone to aliasing distortion, so the brightness isn't all too good effect. BarbaBatch provides the best balance of brightness and low noise.

Compositing to Quicktime

If your goal is to produce a QuickTime sound-track, you can proceed in a couple of ways. If you produced the audio while synced to a QuickTime clip in one of the multitrack programs, you might render a mix to 16-bit, 44.1 kHz, convert it to a more compact format using a separate format conversion program, and composite the converted file with the video soundtrack using Apple Movieplayer (freeware) or similar QuickTime editor. Alternatively you might take advantage of WaveConvert's unique ability to process audio tracks that are already part of a QuickTime movie. Then, in WaveConvert, specify the QuickTime movie as an input file. The program will extract the audio track, process it, and re-composite it in one step. Unfortunately QuickTime movies written by WaveConvert aren't ideal. Using Apple Movie Analyser, you can see that WaveConvert doesn't interleave the new audio track with the video track, making it more difficult for the delivery platform to maintain audio/video sync and continuous playback. Also, the old audio track is still there - although you can't hear it- making the movie much larger than necessary. A Movie like this requires cleaning up in a utility like Terran MovieCleaner ($195) or Apple Movieshop (freeware) before it can be put to use in an interactive project. Fortunately, the multitrack programs discussed in part 1 let you select the destination audio format when you export a QuickTime movie, including Opcode Digitrax (MIX TO MOVIE...), and MacroMedia Deck II (EXPORT TO MOVIE...) Compared with dedicated format conversion programs, DigiTrax produces the least satisfactory results, introducing aliasing distortion. Session does a decent job if you set SAMPLE RATE CONVERTOR QUALITY to HIGHEST. For best results use the SQUEEZING conversion option with SCALE BOUNCE - but even so, session's format conversion doesn't sound quite as good as BarbaBatch's or WaveConvert's, Deck II's on the other hand, is very good indeed. Check ADD AUDIO TO MOVIE, select an output file format, and select CONVERGENT ROUNDING. The results sound better than WaveConvert's but not quite as good as BarbaBatch's.When you're producing QuickTime clips, there is more top it than getting the sound and image right. The movie must be flattened and the media tracks must be interleaved - and as you can see, even a very capable audio program like WaveConvert can have trouble in this area. Deck II is the only program of the bunch that that offer standard QuickTime save options when you compile a movie, like MAKE SELF-CONTAINED and MAKE PLAYABLE ON NON-APPLE COMPUTERS. Both Session and DigiTrax can make a movie self-contained, but only Deck II moves the track headers from the resource fork to the data fork, preparing the movie for playback on Windows systems. The Final QuickTime trick is is ending up with a movie of the proper length. Assuming the video is in finished form, you'll want to preserve the original clip's frame rate and length. Unfortunately, Session and Digitrax set the movies length to that of the longest audio track you're mixing. If the audio program is shorter, the video will be truncated; if it is longer the video will be padded with white frames. For the most part, Deck II respects the length of the original video track - if the audio program is too long, it'll add a single white frame at the end.

Finishing Touches

One step remains :creating small fade-in at the beginning and a small fade-out at the end of every file. These fades should be short (50 ms - 100 ms depending on the sharpness of the initial attack). In fact, they should be imperceptible. The point is to make sure that all files begin and end at zero level. This keeps pops and other extraneous noises from occurring as playback jumps from one file to the next. BarbaBatch include automatic fade-in and -out among it's options. If you use a different format conversion program a good time to add these fades is when you open each file for final verification. In any case it must be done after conversion to the destination format. This is because during the conversion certain calculations can render smooth fade inaccurately , leaving a non zero amplitude at the beginning or ending. (Note frome Audio Ease:the automatic fading in BarbaBatch is indeed done after the mentioned calculations)

The Big Picture

This series of articles has covered a number of tools that make it possible to produce professional audio assets on the desktop and adapt these assets for use in interactive projects. By relating the tools to specific steps in the production process, it's easier to see the role each program can play in making high impact audio for the web, CD-ROM, and other interactive delivery methods. Taking a step back let's try to size them up in a more general way. Of the multitrack tools Deck II stands out for both it's power and it's multimedia functionality. The combination of high quality onboard effects and compatibility with Adobe premiere plug-ins sets it apart from session and DigiTrax. Session delivers some unique capabilities of its own, but on the whole it seems better suited to a music production environment. DigiTrax works well, but it's a simpler program with far fewer power-user features. Furthermore neither Session nor DigiTrax does a good job converting high-res audio files into more compact formats. Deck II boasts a rare combination of flexibility and functionality - that is, it suits a wide range of needs very well. And it's the only program that exports QuickTime movies fully ready for integration into an interactive project. Is it possible to do everything described in this series substituting a stereo editor for the multitrack program? Stereo editors like SoundEdit 16 Alchemy and Audioshop do offer similar functionality, and they have some advantages - on the whole they're simpler to use, less costly, and don't require a high-powered computer But destructive editing becomes a problem when you're dealing with long audio segments. Frequently the entire file must be recomputed when you make the slightest change. Beyond that, realtime mixing and sync to QuickTime are valuable productivity features. Although SoundEdit 16 has these capabilities to a degree, it's not in Deck II's league in this regard. Among stereo editors, Peak's non destructive editing helps bridge the gap. Moreover, Peak and Deck II are the only programs that can export regions as individual files, a real boon when it comes to managing the explosion of small files that can characterise an interactive production. Peak and Deck II alone support Premiere Plug-Ins, making Invision's CyberSound suite a worthwhile complement to either program. Deck II duplicates some of cybersound's effects with a higher degree of integration, but it lacks others such as compression, phasing, flanging, and multitap delay.

Peak has fewer built-in effects, making cybersound even more useful. However, the quality of Cybersound's effects isn't quite studio-grade. Waves plug-ins, on the other hand, actually bring pro audio to the desktop. Their audio quality is top-notch and their user interfaces are very clear and detailed. Some of these effects are too advanced for audio dilettantes. This isn't a fault, but an indication of the art of sound recording. Others are simpler. The ultimate interactive audio arsenal would include Waves AudioTrack and L1. With these additions, Peak and Deck II become thoroughly professional tools. The Various format conversion programs simplify and automate one of the most critical tasks in the process. S/Link has a straightforward user-interface that's convenient for dealing with files in complex hierarchy. Automator is nice (not to mention free) , but the fact that it's simply an AppleScript command centre makes it slow and a little less robust for serious batch processing.

WaveConvert and BarbaBatch add crucial dynamics processing features. Too bad BarbaBatch doesn't play files; otherwise it is the most effective format conversion program, delivering excellent speed, quality and ease of use. (note from Audio Ease:The reviewer was working with a pre-release. In fact, BarbaBatch 2.0 incorporates a batch auditioning tool that plays all 13 formats with adjustable speed and separator sounds) . A Solid Audio setup for Macintosh-based studios, then, would include Deck II, Peak, AudioTrack, and BarbaBatch. With these programs working together, the benefits of common file formats and plug-in standards become obvious and computer-based audio production begins to fulfil its promise. The remarkable thing is the absolute sound quality of these tools. The results they deliver required a high-end studio only five years ago. Even as recently as last year, combining various tools and applying them to interactive productions bordered on black-magic. Today things go pretty smoothly. With bandwidth and storage space becoming more plentiful, audio isn't likely to remain in the background for long. It's time to grab the tools and make big noise.

 About the Author

Atau Tanaka, who has served as principle developer on CD-ROM titles for Time-Warner Interactive and Voyager, currently performs with the trio sensorband using interactive interface technology to control music and real time image synthesis. His Paris Based team Bionic Media created the Web site Witness (http://zeep.com/atau) for WorldmediaLive and the U.N.