Digital Audio Labs cardD

Wanna record professional quality audio on your PC's hard disk? Brian Heywood investigates the temptingly low cost route offered by Digital Audio Labs' plug‑in CardD system.

Given the growing interest in hard disk recording, any system that can deliver professional quality audio for around £1,000 is certainly worth a closer look. The CardD from Digital Audio Labs is a two‑channel system, based on two PC expansion cards, and can be used with a variety of different software editing packages. What makes a system 'professional' can be a bit unclear; my own personal rule of thumb is whether it has a digital audio interface (either AES/EBU or SPDIF) so that you can transfer the audio between DAT and hard disk without going through an analogue signal path. The CardD is the cheapest system that I know of which has the option of a digital interface.

Windows MPC

Although the CardD has been around for a while in the form of a low cost hard disk recording system for the PC, it's only recently jumped on the Windows multimedia bandwagon. There is a distinct difference between hard disk recording and using a Windows MPC sound card to perform audio production work. This might seem a rather odd thing to say, since both sets of technologies are performing more‑or‑less the same tasks — namely, recording and playing back audio data on a PC's hard disk.

However, there are a number of reasons why I say this, having had to work with both types of system. Most of the differences between the two technologies boil down to speed of operation of the editing software. A professional hard disk recorder like SADiE, Soundscape or the Session 8 all utilise DSP (Digital Signal Processing) technology and dedicated hard disks to get the best performance out of the system and speed up the editing of the audio data. Dedicated systems also use various tricks to speed up the editing process, such as employing low resolution sound 'profiles' for displaying waveforms and other techniques inherited from the studio control room.

On the other hand, MPC sound cards try to approach the middle ground by providing the basic functions at a competitive price, with performance and sound quality losing out. So most cards don't incorporate DSPs (Turtlebeach's Multisound, the Gravis UltraSound and Soundblaster Pro 16 ASP being the notable exceptions). Significantly, the lack of a DSP means that the editing software has to rely on the PC's processor to do all the hard work, which is not an ideal situation since it is not optimised for signal processing. Furthermore, the performance of a MPC‑based system is restricted by the relatively slow hard disk interface found on the PC, which also limits the number of 'CD quality' digital audio channels to two, ie. a single stereo pair. The last major failing of Windows MPC systems — at least for professional use — is the lack of a digital interface (either SPDIF or AES/EBU) for transferring the material to and from the ubiquitous DAT machine.

Digital Connection

The CardD system from Digital Audio Labs (DAL) fills the gap between the low‑end professional systems and the sound capabilities of a 16‑bit MPC Windows sound card. CardD provides professional quality converters on two channels of digital audio, with the option of an SPDIF digital interface, for around a third the price of the cheapest comparable professional system. Unlike comparable 'pro' hard disk recorders, DAL don't tie you to using a particular digital audio editor; you can choose between a number of recommended editors (the front end) or use DAL's own EdDitor software. In fact, you can use any MPC‑compatible audio editor, since DAL thoughtfully provide MPC drivers for the CardD. This means you could use your existing MPC software, if you have some, and simply use the CardD hardware to upgrade your setup to professional quality sound with a digital interface.

What's the catch? Well, the main items missing from the CardD recipe are a Digital Signal Processor (DSP) and a dedicated disk interface. The lack of these two features means that the performance of the CardD system will be inferior to a professional system in every aspect bar one (which happens to be the most important one) — sound quality. So, in effect, DAL have left off the icing and decorations but have kept the substance of the cake, allowing you to produce professional quality audio. I have been looking forward to reviewing the CardD for a while now; let's see if it lives up to its promise.

The Hard Part

The system reviewed here is based on the fully expanded configuration with the digital input/output option. The hardware consists of two interface cards that slot into the PC's expansion bus; a 16‑bit card containing the audio connectors and converters, and an 8‑bit card for the digital interface. The two cards need to be installed near each other — as they are interconnected by a short ribbon cable — and away from other electrically 'noisy' cards, such as video and hard disk controllers. In my system they were installed on either side of a Voyetra MIDI interface without problems.

The audio card is a 16‑bit, half length card which has the audio connectors — two in, two out — on the metal back plate. The connectors are standard phono (RCA 'cinch' type) and can be individually configured between +4dB (professional), ‑10dB, or CD consumer line levels. The inputs can also be configured to record down to DC, although for normal audio applications you will want to stay with the factory preset values, which give a flat frequency response from 20Hz to 20kHz. The only other configuration item on the card is the base address, which should only be touched if the default setting clashes with another card installed in your PC. The audio specification puts the dynamic range at 92dB (typical), but as with all such figures you have to treat this with a bit of caution, since other factors — such as the quality of the PC's power supply — will affect the actual performance.

The Digital Audio Interface card is the same size as the converter card, but only requires an 8‑bit slot. There is only one setting on this second card, which is used to ensure that both cards use the same base address. The review cards both installed without any problems; the only alterations I made were to set the audio inputs to +4dB to match my mixing desk.

Like most sound cards, the CardD uses both an IRQ and DMA channels to communicate with the software and transfer data to and from the hard disk. DAL provide a DOS program for configuring the CardD and testing the recording and playback features of the card. The CardD defaults to using IRQ 7 and DMA channels 5 and 6, which worked in my PC without problems and should suit most PC configurations. One point that DAL say you should look for is that certain cards — like some SCSI cards, for instance — run in 'bus master mode', which means that the DAL software can't access the computer's data bus fast enough when recording and playing back audio data. Usually the drivers can be altered to co‑exist with the CardD, but it's worth mentioning this to your CardD dealer if you have a SCSI card in your PC.

Soft Options

The CardD hardware is supplied with only a very basic program for configuring and testing purposes, so you will also need to get hold of some kind of audio editing software. As I mentioned earlier, the CardD is supplied with a Windows 3.1 audio device driver, so you can use any MPC‑compatible .WAV file editor, such as Turtlebeach's Wave For Windows.

The software supplied for the review was DAL's recommended editor, called the EdDitor. It actually consists of three Windows 3.1 applications; a Digital Audio Display editor, a Playlist editor, and a Catalog editor. The first is a fairly conventional waveform‑based editor which allows you to record, playback, mix, modify, and generally hack around the digital audio data stored on your hard disk. The Catalog editor lets you assign sound clips to graphic buttons on your PC's screens, allowing you to fire them off using the mouse or a MIDI keyboard. The Playlist editor lets you set up lists of sound clips that can be fired off either sequentially, on cues, or according to a SMPTE time.

The software is installed using a Windows Setup script, which copies the files onto your hard disk and creates a program group for the three applications. The installation process lets you choose where the program and sound files are to be stored and how much space they require. The system comes with about 8 megabytes of sound data, used for the demonstration tutorials, but the all‑important program files only take up just under half a megabyte of hard disk space. DAL recommend that you have at least 200 megabytes of hard disk space available, which will give you around 20 minutes of stereo sound. To elicit the best performance from the system, DAL suggest that you allocate a separate disk partition for holding the sound files, as this will reduce fragmentation. However, they also suggest that you use a disk compactor like SpeeDisk (Norton Utilities) or Compactor (PC Tools) periodically.

Using The Editor

The EdDitor software is based around two windows, depicting the waveform data; the lower one shows the source data and is 'read only', while the upper window shows the current output wave file (ie. the results of the current series of edits) and is referred to as the Modify window. To create a new sound file, you load the raw sound data into the lower window then select the portions that you want to retain, copying them into the appropriate position in the upper window. You can merge the data in a number of ways, either by mixing the new data into the waveform currently displayed in the upper window or by performing crossfades etc. The EdDitor uses Windows .WAV files to hold its sound data, so you could use the resulting files as part of a multimedia PC presentation or even import them into another editing application at a later date, if you wish.

The editor can operate in one of two modes, the first being called 'Cut‑and‑paste' mode and the second 'Editlist'. In 'Cut‑and‑paste' the contents of the Modify window are saved as a single digital audio .WAV file, essentially a snapshot of the edits at the time you save the file. The Editlist feature saves the contents of the Modify window as a set of pointers to the original sound data files, thus avoiding duplication of the data on disk; any temporary files containing crossfades, EQ, or any 'processed' sound are saved for later use.

The EdDitor offers a number of tools for altering all or part of the recorded sound data, performing the operation, then transparently saving the result as a temporary file. The tools let you mix the data from two sound files in various ways, alter the gain or equalisation and even reverse the sample. These tools are pretty basic — for instance, the EQ is only a simple shelving bass and treble control — but they do allow you to tweak the data after it has been recorded onto disk. The program also allows you to 'undo' the last 10 operations, selecting from a 'history' list of edits, so you can easily change your mind if you want.

When compared to a standard MPC waveform editor the EdDitor's performance is very quick, due to its use of 'metafiles' to display the waveform data. For each sound file there is an associated metafile, which holds a simplified version of the waveform data; since these files are less than one percent of the size of the full‑blown audio data files, the screen display updates are much faster than editors that display waveforms from the actual data. The audio processing tools also seem to work about 10 times faster than the equivalent functions in my copy of Wave For Windows, for example, although whether this is due to a simpler algorithm or tighter coding is impossible to say. Most of the processing functions seem to take about twice real time; for instance, it took about six minutes to normalise a three‑minute track. The actual performance will probably vary according to how powerful your PC is (the review machine was a 50MHz, 386DX with 4Mb of RAM).

Catalog & Playlist Editors

As well as the main EdDitor software, you receive two smaller applications that allow you to use the CardD for tasks other than assembly editing of recorded material. The first, the Catalog editor, allows you to set up a page of 'buttons' on your PC screen, each one firing off a different audio sample; alternatively, each button can be associated with a key on a MIDI keyboard. This would be especially useful for theatre work, where you could use it to trigger sound effects at the appropriate times. One caveat though: in common with all MPC sound cards, CardD can only play one sound at a time, so you can't have two samples playing simultaneously — the first sound will always 'cut off' when the second starts to play.

The second application, the Playlist editor, allows you to set up a list of sound files that can be played back in a particular order, either under user control or triggered externally via SMPTE timecode. This too could be used for firing off sound effects, although it still has the same restriction of not being able to play two sounds at once.

Digital Interface

One of the main features of the CardD is the digital interface, which allows you to transfer your audio data to (and from) the PC in the digital domain. This means that you can take material directly off DAT or CD (provided these machines have a digital output, of course) without losing any quality. The I/O card uses standard phono (RCA 'cinch') sockets, which is a common format for consumer equipment, and the interface can be clocked internally or slaved to the incoming SPDIF signal. The EdDitor software allows you to choose the audio source from within the Options menu, as well as letting you define the state of the 'copy protect' and 'pre‑emphasis' bits in the digital data stream. All these settings are also accessible from the Drivers section of the Windows Control Panel, so that you can set them for any MPC wave editor.

Time, Gentlemen, Please...

You can use timecode with the EdDitor and Playlist as long as you have a MIDI interface and some kind of SMPTE capability. This means either a card with a SMPTE input — like the Voyetra V24s or one of the Music Quest cards — or a way of generating MIDI Time Code. Since the sample rate of the CardD is fixed at the standard rates, the best you'll ever get out of the system is 'trigger lock'. This means that you can start playback of a sound file at a particular time, but thereafter it will free‑wheel; in other words it will not track any variations in the incoming timecode. This shouldn't be a problem if you are using short sound segments, but a long music bed or rhythm track will gradually get out of step if you are synchronising the CardD to a tape transport (say, a video machine).

How well your Windows sequencer integrates with the digital audio editing software will depend to a certain extent on the capabilities of the various applications. DAL provide a MIDI driver — called the MIDItasker — that lets the software eavesdrop on a particular MIDI channel for synchronisation and note information. One point you should be aware of — since all the audio processing is performed by the PC's processor, you could encounter performance problems (especially if you use Cubase, which places a very high load on the PC).

Verdict

For some people the CardD will be like manna from heaven, offering a complete audio system with digital I/O for around £1000 — or less if you already have a .WAV file editor — but you should be aware of the system's limitations. When compared to the other, admittedly more expensive, PC hard disk systems I've reviewed lately in SOS (SADiE, Soundscape, Session 8), CardD is very much the poor relation — it's slower, limited to two outputs, and unable to continuously resynchronise to incoming SMPTE timecode. However, when compared to Windows MPC sound systems it is blindingly fast, has digital I/O and does at least offer some synchronisation facilities. The CardD also sounds pretty good and can operate at professional line levels (+4dB) if required. I could imagine using it for general multimedia work and for compiling things like short radio spots, voiceovers or adverts — as long as I didn't have to do it too often. The CardD EdDitor would also be a good choice for mastering from DAT if you're strapped for cash, allowing you to perform crossfades, fadeouts, and generally control the order of tracks, provided you have enough disk space to hold the data files.

One major advantage of the CardD is that you're not tied to a particular software vendor, so you will be able to take advantage of any advances in MPC disk editing software (such as the Software Audio Workshop software: see 'Multitrack Use' box). The CardD is certainly worth looking at if you need a budget hard disk recording system... but don't expect it to deliver the same level of performance as a dedicated professional system.