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Digidesign Pro Tools 24

Digital Recording & Editing Environment By Mike Collins
Published February 1998

Digidesign Pro Tools 24

Pro Tools has made the leap to 24‑bit, but does the increased theoretical quality really translate to a better sound, and is it worth the extra money? Mike Collins finds out.

What did you get for Christmas, then? I got a brand‑new Pro Tools 24 24‑bit hard disk recording system (previewed in the last issue of SOS), a Power Macintosh 9600/350, and a Rorke Data AVR35 9Gb removable hard drive system with an Atto ExpressPCI SCSI accelerator card — on loan! This little lot arrived at my flat by Christmas Eve, just in time for me to put the system into my car and drive off to spend Christmas with my family.

SInce I was going to be looking at the system over Christmas, I decided to bring a couple of guitars and an amp, so I would have something to record. I also took some mics and a Mackie 1604 mixer, plus a pair of small monitors.

I'm on something of an anti‑MIDI kick at the moment, so what I want from a DAW [Digital Audio Workstation] is something which will capture as true and accurate a representation as possible of the acoustic and electric instruments I love to play and record. Over Christmas there would be no shortage of raw material to record — my family and many friends in the area both sing and play various instruments. The main questions for me would be:

  • How does the Pro Tools 24 system compare with the PTIII/888 combination I have in my studio?
  • How natural a sound can I capture using the 888|24 interface?
  • How suitable is the Rorke Data removable hard drive for use with PT24?
  • How suitable is the Mac 9600/350 for the system, and how well does it compare with my 9500/132?

Since the new features of the Pro Tools 4.1 software supplied with the system were detailed in last month's preview, I won't be covering them again in this review; instead I'll be focusing on the above considerations.

The Review System

Digidesign Pro Tools 24

The PT24 'core' system consists of the new d24 half‑length PCI card, a DSP Farm PCI card, and the Pro Tools 4.1 software. The card can handle 24 tracks of 24‑bit audio, although by the time you read this a DAE software update should be available which will enable it to handle 32 tracks. The 888/24 interface uses Crystal A/D and D/A converters (dynamic range of 110dB for the A/Ds and 102dB for the D/As, according to Digidesign). The new interface is virtually identical to the 888 interface in most other respects, although it can now be used in stand‑alone mode without being connected to the computer.

The computer I was lent for the review uses a 604 processor running at a clock speed of 350MHz and came fitted with 64Mb of RAM, a 4Gb internal hard drive, a CD‑ROM drive and a Zip drive. The processor speed of this computer means that users should have no trouble in working with many tracks of audio and carrying out intensive signal‑processing with ease, while the internal drive has enough speed and capacity to provide at least 16 tracks of audio on reasonably‑sized projects. The data rate necessary to achieve full 24‑track, 24‑bit performance is 3.6Mb per second of sustained throughput, and for this a SCSI accelerator card and a fast, 'Ultra‑wide' SCSI hard drive are required. This last point means that a 6‑slot PowerMac would also be required, because Pro Tools does not support the use of SCSI accelerator cards on 3‑slot machines. In addition, 64Mb is the absolute minimum amount of RAM for Pro Tools 4.1 software. The PowerMac 9600/350 certainly seems to have the right specifications.

I immediately noticed that the 9600 was much faster and more responsive than my 9500/132. Microsoft Word opened virtually instantly, while the Pro Tools 4.1 software opened in about 13 seconds with just the standard set of supplied plug‑ins. The case is a new design from Apple's in‑house team which allows much better ease of access than on previous models, making it much easier to swap PCI cards around, add extra RAM and so forth, and the 9600 also features a much quieter cooling fan. The Mac II used to make an extremely annoying whirring and whining sound, while the Quadra 950 whined less annoyingly, but still whirred very audibly. The 9500 is a great improvement, but you would still be very reluctant to record anything in the same room with a microphone anywhere near the Mac. The noise of the 9600's fan is now so low that it would not bother me in anything but the most critical of listening situations.

The Rorke Data removable hard drive system has a very rugged 19‑inch rackmountable metal case with space for a pair of drives; it came fitted with one drive, capacity 9Gb, which worked out to about 8.5Gb formatted. Running off the Atto SCSI accelerator card, this was extremely fast and had no trouble playing back 24 tracks of music. Unfortunately, the fan noise was so loud and obnoxious that I had to turn the Rorke drive off and use the internal drive for the quieter recordings.

In Action

Digidesign Pro Tools 24

I had already tried out the microphones I had brought along with my PTIII/Yamaha 02R/PowerMac 9500 system at home, and knew that all three (the Neumann M149, the AKG C12 VR and the Calrec Soundfield Mk IV) were capable of feeding the highest quality of audio possible into the 888/24 interface. I used the C12 to record electric guitar, the M149 for acoustic guitar, percussion, harmonica and vocals, and the Soundfield as a stereo microphone for piano and harp.

To test how many tracks the Rorke drive could support, I used a demo song supplied on the Pro Tools CD‑ROM. This already had 15 tracks of audio, so I recorded a further nine tracks — five tracks of rhythm and lead guitar, a couple of tracks of maraccas, and a couple of tracks of tambourine. I did encounter a couple of strange happenings, such as the guitar take where the recording simply stopped after about a minute for no apparent reason, with no‑one close enough to have touched the controls by accident or anything like that. But when I found myself playing back track 24 along with all the other 23 tracks, I was convinced! The Rorke drive and Atto SCSI card combination has to be one of the fastest systems I have actually used, and the Rorke drive is built like a tank.

A friend of mine plays blues and R&B harmonica, so I accompanied him on electric or acoustic guitar and we recorded several pieces. Listening back, it was obvious even through the small multimedia speakers I had brought along that the 888/24 had made a first‑rate job of digitising the output from the M149 mic. The clarity and naturalness of the sound was simply superb, and the 888/24 acquitted itself very favourably as an A/D converter, capturing the recordings onto the hard disk faultlessly.

For some low‑key recordings of solo harp, piano and voice I found the Rorke drive unbelievably noisy, so for these recordings I had to dispense with the Rorke and record to the internal 4Gb drive in the 9600/350. At this point I came to appreciate that Digidesign's decision to stop using their own SCSI system on their Pro Tools cards — thus allowing any SCSI drive connected to the Mac to be used for recording and/or playback — makes the system much more versatile than it was while users were restricted to using drives connected to the Digidesign SCSI buss.

...if you're recording audio with a very wide dynamic range, such as classical music, you will value the extra dynamic range of 24‑bit.

Is It A Winner?

In short, yes. Everyone who heard the results agreed that the recordings made with the PT24 system sounded very natural and transparent, with all the nuances of the harp, piano, acoustic and electric guitars, harmonica and vocals faithfully captured and reproduced. Compared with my 16‑bit PTIII/888 system, everything sounded clearer and more detailed. The converters in the 888|24 interface were undoubtedly responsible for capturing and reproducing this fine sound quality, and, for me, there was no question that this new interface is a significant improvement over its predecessor. The PowerMac 9600/350 is a dream machine with the speed and expandability you need to run a Pro Tools 24 system professionally. The Rorke Data removable hard drive is ideal for studio use, especially if situated in a separate machine room, and appears rugged enough to take on the road, for use in mobile or live situations. It has plenty of capacity and bags of speed, and the only downside is the noise of the fans. Finally, compared with the PTIII/888 combination, which I own, the PT24 system now offers double the number of tracks, with 32 rather than 16, while the 888/24 interface will digitise at 24‑bit and monitor at 20‑bit, which accounts for the noticeably better sound quality. And it's comforting to know that I could save files at 24‑bit resolution to help preserve the last ounce of quality right up to the transfer to a 16‑bit medium. So would I like to upgrade as soon as I can afford to? Well, what do you think?

Many thanks to Su Littlefield of Digidesign and David Millar of Apple UK.

Crucial Questions

Paul White primed me with a set of crucial questions to answer — or to ask Digidesign to respond to:

  • Why 24‑bit resolution?

There are various advantages to working in 24‑bit. First of all, you get a much better signal‑to‑noise ratio. The rule of thumb is 6dB per bit, giving you 96dB for 16‑bit, 120dB for 20‑bit and 144dB for 24‑bit. Real‑world systems do not achieve the theoretical maximum S/N ratios at these higher bit‑rates, but they do achieve significantly higher dynamic range than 16‑bit systems. Naturally, if you're recording audio with a very wide dynamic range, such as classical music, you will value the extra dynamic range of 24‑bit. But what if you work with pop music, which typically has much less dynamic range — in other words, it's loud most of the time? Well, the higher resolution of the 24‑bit analogue‑to‑digital conversion will always give you a much more accurate representation of the original analogue audio — so it will sound 'truer' to the original than 16‑bit audio. Of course, with more dynamic range available in the system, you can use some of this as 'headroom' above the nominal 0dB level, to cater for unanticipated peaks in the audio which would otherwise clip — another major advantage.

This extra resolution is particularly valuable on systems that support extensive mixing, because working with higher bit rates/resolution not only helps to create the most accurate image of the original audio source, but also keeps this image clearer throughout the various stages of processing. Complex calculation algorithms are used not only for mixing, but also for signal processing (EQ and the like), so the higher the resolution you start out with and maintain, the less rounding will be required, and therefore the less distortion will result from this.

  • Do you need to use a mixer with Pro Tools?

Given that the mix window has its own very usable built‑in EQs, dynamics and delays, and that plug‑in software versions of many well‑known and respected stand‑alone effects processors are now available, Pro Tools systems will allow you to go into even more detail than conventional mixing methods. You also get truly total automation and recall.

You do need to keep in mind that low‑level microphone or instrument signals will not drive the line‑level inputs on the 888 interfaces successfully, so you will need DI boxes or pre‑amplifiers for these. You can reach the point fairly quickly where it can be more cost‑effective to at least use a small mixer with suitable microphone and instrument‑level inputs — such as the Mackie 1604 or similar. You may also need to monitor other external equipment, such as a CD, DAT or cassette deck, or other instruments, and some kind of small mixer is pretty much essential for this.

There is already a large number of artists and producers, in both the semi‑professional and professional fields, working on PT systems and not using large mixing consoles anymore, or relying on them only for monitoring purposes. Digidesign say they expect to see this kind of usage increase quite dramatically with the advent of the Mackie HUI (now shipping, and previewed in the last issue of SOS) and Digidesign's own forthcoming Pro Control. These controllers make PT's already existing mixing features much more easily accessible, giving engineers and producers the type of console control surface which they are already used to.

  • What are the ramifications of using standard hard drives?

When you choose to work with 24‑bit files you can only record two‑thirds as many tracks for two‑thirds the recording time as when you're working at 16‑bit resolution — onto the same size of hard disk. And if you want to use 24 or 32 tracks of audio, rather than 16, your storage requirements will obviously increase. If you bought your drives last year or the year before, they're likely to be slower and of lower capacity than the latest crop of drives you can buy today for the same money. Also, your bandwidth requirements will increase substantially when working with 24 or 32 tracks of 24‑bit audio, so you'll almost certainly need to use a SCSI acccelerator card, with large‑capacity fast and 'Ultra‑wide' hard disk systems, to achieve the required data throughput from the drives.

  • Can you split the audio over several drives?

Yes, but it's better to keep all the fast drives together on your fastest SCSI buss, with slower ones on the slower internal and external on‑board SCSI busses, remembering that the external SCSI buss is the slower of the two on‑board busses.


  • If someone is upgrading, will they have to get their plug‑ins upgraded?

"Updates for all Digidesign unbundled plug‑ins and the Focusrite d2 are included on the Pro Tools 4.1 CD‑ROM. The Installer will automatically update these plug‑Ins (DINR, DPP1, D‑Verb, D‑Fi, Focusrite d2), if present in the Plug‑Ins folder during your Pro Tools 4.1 installation."

  • Do the plug‑ins work properly at 24‑bit?

Digidesign have tested all the third‑party plug‑ins of consequence and have determined that all these work with 24‑bit resolution — except for Intelligent Devices IQ. Ed Gray, Digidesign's Development Partners Manager, explains: "We did not test the third‑party plug‑ins as fully as we would test a Digidesign plug‑in such as D‑Verb. Rather, our software engineers had a cursory chance to fire them up and look at them in PT24 systems. Remember, the DSP Farms on which the plug‑in processing takes place have not changed, so all third‑party plug‑ins appear to work fine on PT24. IQ is the only plug‑in we know of that does not exploit the 24‑bit capability of Pro Tools 24. And since Intelligent Devices is no longer a Digidesign developer, they have no plans to upgrade either their AD1 or IQ."

  • Are Digidesign including any alternative dithering algorithms with PT24?

"Not at present."

  • Will Sound Designer II work on this hardware?


  • Will the ADAT interface work with PT24, or will this need to be upgraded?

"Pro Tools 24 does not support the Digidesign ADAT Interface. This is not possible because the new Pro Tools 24 system hardware uses a 24‑bit system word clock. Unlike Pro Tools III, it is not switchable between 24‑ and 16‑bit word clocks. The Digidesign ADAT Interface requires a 16‑bit word clock for operation, therefore it cannot be supported with Pro Tools 24 systems. Digidesign will introduce the ADAT Bridge at NAMM with a product release within the first quarter of '98. This will address the need for ADAT/PT synchronisation and will also support the new 20‑bit ADAT."

  • What about expansion chassis support?

"PT24 supports both the 7‑ and 13‑slot Bit‑3 expansion chassis. It does not, however, support the Magma chassis."

My Wishlist

One of the first questions I was asked — by my brother, who is not involved in recording work — was why there was no reverb supplied with the basic system. He works as a DJ, occasionally does 'live' sound for bands and has come across audio mixers with built‑in reverb, so he assumed that there would be at least a basic reverb supplied with Pro Tools. A fair question, I reckon.

It would also be nice if you could add stereo tracks rather than just mono ones. Currently, to assign a stereo plug‑in to a stereo pair, you have to 'roll your own' stereo track with an aux input and a pair of busses, which is a waste of DSP and not very convenient.

Personally, I was hoping that MasterList CD might have been incorporated into the Pro Tools software. Perhaps it could be linked in as a plug‑in, or something of the sort? And, for me, it would be much better if there was a list editor in Pro Tools which would allow you to quickly and accurately adjust the positions of regions numerically. This is available in all the MIDI + Audio software packages.

'Undos' are still limited to one level, and (more importantly) are not implemented for anywhere near all functions. Also, although the real‑time features have been improved, so that you can now Save while playing back, you still cannot rename files while playing these back — which was one of the first things I wanted to do after a busy recording session where I had no time to name things as I went along. And you can't change the display in the Edit window to show a waveform instead of blocks, or a volume/pan graph, or access various other features, while the system is playing back.


  • You can now work at 24‑bit resolution.
  • 24 tracks are now available, and 32 tracks with the next software update.


  • Users upgrading from previous versions will probably have to shell out for more up‑to‑date, faster hard drives, on top of the upgrade price.
  • Lack of multiple Undos.


Pro Tools has come of age, in the sense that it is now a fully‑fledged 24‑32 track recording device. The sound quality of the converters has similarly been lifted to professional levels of excellence. The possibility now exists to run a complete recording/mixing/signal processing environment in software, especially with the addition of a hardware controller such as the Mackie HUI, which may well allow you to do without an external mixer.