One year ago, I reviewed Pro Tools 4.0. I am still just as impressed as I was then. Now comes version 4.1 and some new hardware to go with it.

A Bit Better

The most notable improvement in Pro Tools 4.1 software is support for 24 bit files. Other software enhancements include automated Plug-in bypass and improvements in AudioSuite Plug-ins. The hardware interface improvements include a new d24 PCI interface card, a new 24 bit version of the 888/24 bit I/O box, support of the Mackie HUI control surface, direct support for the new Universal Slave Driver for SMPTE synchronization, and MIDI Machine Control of Pro Tools transport functions.

A 24 bit Primer

To better understand the significance of 24 bit capability, I need to talk a little bit about why more bits are better. One improvement is in the signal-to-noise ratio of 24 bit. You get roughly 6 dB of signal-to-noise ratio per bit. This is where the 96 dB figure comes from when you read about 16 bit. With 20 bit material, this figure jumps to 120 dB, and 24 bit pushes the signal-to-noise ratio up to a whopping 144 dB.

Without question, 24 bit is definitely better than 16 bit, but the response I get most of the time is “What the Hell difference does it make? I am recording guitars and air conditioners and stuff that is not that quiet.” Very true. And except for very special circumstances, like the decay of an acoustic piano chord on an audiophile recording, it doesn’t matter. The part of 24 bit that does matter, is resolution.

The bit resolution determines the amount of “fineness” that is used when recording the analog signal. It works just like digital picture resolution. The picture you see on the LCD display of the camera looks good, but when you copy it over to your computer and display it full screen straight lines become jagged. These straight lines in the picture correspond to the waveforms of the analog audio signal, especially the low frequencies. A 20 bit signal has 16 times better resolution than 16 bit, while a 24 bit signal has 256 times more resolution. This holds true over the entire dynamic range. The loudest part of the recording contains just as much accuracy as the lowest level signal.

One additional plus from 24 bit recording is that you can lower your “Zero” reference so that you have more headroom. Headroom is the amount of room you have above Zero level for those unexpected peaks that show up every so often. If you lower the reference by 6 dB, you still maintain a 138 dB signal-to-noise ratio and have 20 dB of headroom.

The difference in sound quality between 24 bit and 16 bit is not some small difference that requires training. You can hear it on the first comparison with any kind of music, with one hand tied behind your back. The difference you will notice the most is the tightness of the bottom end, and the enhanced detail of the images. A vocal recording with one microphone sounds three dimensional.

The New Hardware

As mentioned above, the 24 bit core system comes with a new interface card, the d24, a DSP farm card, an 888/24 interface, and all of the necessary Pro Tools 4.1 software. The d24 card will connect to one or two interface boxes (with the addition of an optional Y cable). The interface boxes can be any mixture of the new 888/24, a standard 888, or the economical 882 interface. The connector on the DSP Farm allows you to connect to a third interface box for a total of 24 tracks of simultaneous I/O. Existing 888 interface boxes can be upgraded to 888/24 at the factory if you are upgrading a current system.

The new 888/24 audio interface contains 24 bit A/D converters for all analog inputs, while the DA output section contains only 20 bit converters. This is meant to keep the cost down, as 24 bit DA converters are currently priced near that of small condominiums. Also, you seldom ever need to output multiple tracks analogly (new word) at 24 bit resolution. You will most likely be interfacing digitally which supports the full 24 bit stream.

To me, the biggest change in the new system is that the hard disks now resides on the Mac SCSI bus instead of being connected to the Disk I/O card. This means that backup, file transfer and formatting are easier.

One thing that I think you must add to your new 24 bit system is the Adaptec 2940 or 3940 SCSI accelerator for PCI bus computers. If you are going to be doing 24 or 32 tracks of 24 bit recording with lots of edits, it is going to be hard for the Mac’s built-in SCSI controller to keep up. With the addition of the accelerator card, all of your worries are gone. If you ever paid attention to disk access activity with the old system, the disk access light remains on for 70% to 99% of the time, and on very complex situations with fragmented disks, the drives couldn’t keep up. With an accelerator card, the disk access light is only on 20% to 50% of the time. Plenty of overhead for those times when the number of edits gets out of control.

Slot Miser

The new d24 core system requires only two card slots for 24 channels of I/O. As I am writing this, Digidesign has qualified the new three slot Mac G3 Mini Tower for use with the core system. This cuts over $1000 off the price of the computer needed to power the system. With only two slots necessary in the core system, the need for an expansion chassis to accommodate multiple cards is less likely.

First & Second Impressions

If you have followed my columns, you know that I used the 24 bit system for the new Bela Fleck & The Flecktones album in the middle of October ‘97. This system had 24 channels of 24 bit I/O, the Adaptec 3940 SCSI accelerator, and was in a Mac 9600/250 with dual 20 inch video monitors. Installation on that system was unbelievably easy. Insert the CD-ROM, click on INSTALL, and come back in a few minutes. On initial boot, you select which I/O boxes are connected to which ports, and go to work. No glitches, no crashes, recording 24 channels of 24 bit audio 12 hours per day for a week. Upon completion of the recording, Bela proceeded to start editing and overdubbing.

Because we are talking about hard disk recording, I must mention the dreaded “BACKUP.” Only so much stuff will fit on a hard disk. The key to backup for me is speed. For the Bela sessions we had to be able to backup lots of data fast. We used a DLT drive and another computer. While we were recording on one pair of drives, we were backing up the previously recorded pair.

My second impression held up. I just installed a d24 core system with one 888/24, one 888, and one 882 interface. This allows me to get into the 24 bit system and upgrade as the budget allows. I added the Digidesign Universal Slave Driver for synchronization, and the Adaptec 2940 accelerator card for fast disk I/O. The host computer is a Mac 9600/300. With the 350 mHz version out and the G3s on the way, I was able to get a good deal on it.

The installation was just as easy as Bela’s, and I had all of the hardware and software up and running in about 2 1/2 hours. The hardest part of the whole deal was SCSI cables and the Adaptec accelerator. Because of the enhanced speed, cable quality and length are even more important than normal SCSI connections.

Finally

Finally, every man’s Pro Tools. They say you can’t be all things to all people, but the d24/ Pro Tools 4.1 combination comes as close as you can get.

For pro projects I have done in the past, multitrack editing was usually done with two Sony 3348 48 track machines. For the next Steely Dan project, it looks like the recordings will be Sony 3348-HR (48 tracks of 24 bit), the tracks that require editing will be transferred to 24 bit Pro Tools for full 24 bit editing, and the results transferred back digitally to the 3348-HR. How sweet it is.

I have been waiting for this level of hard disk recording for 10 years. I’m glad that Digidesign has helped it arrive with their new 24 carat, I mean bit, system.