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Mark of the Unicorn, Inc. (MOTU) today announced the 24i, a 24-input analog audio interface for computers that will be sold both as an expander ($1195) for 2408 and 1224 hard disk recording systems and as a complete core system ($1495) for Mac OS and Windows 95/98.

The 24i fulfills the vision of computer-based hard disk recording in a cost-effective space-saving single rack-space I/O unit, allowing users to bring all of their outboard gear into the computer via high-quality 24-bit converters to record, edit, mix and master audio recordings entirely inside the computer. The 24i is ideal for recording and mixing synthesizers, samplers, drum machines, tone modules, and the many other sound sources found in today's recording studio.

Designed specifically for multitrack audio production entirely within a host computer, the single rack space 24i provides 24 balanced (TRS) phone jack inputs equipped with state-of-the-art 24-bit A/D converters to simultaneously record 24 channels of 44.1 or 48 kHz audio. For stereo monitoring, the unit's main outputs are supplied in three different audio formats: 24-bit balanced TRS phone jacks (analog), 24-bit optical S/PDIF (TOSLink), and 24-bit RCA S/PDIF (coax). The 24i includes ASIO, Wave and Sound Manager drivers for compatibility with all of today's popular audio software on both platforms and the core system ships with AudioDesk, MOTU's sample-accurate audio workstation software for Mac OS.

"Computers are now fast enough to easily handle entire multitrack recording projects — from initial tracking to final mastering - completely inside the computer," says Jim Cooper, Director of Marketing at MOTU. "But until now, getting enough direct analog audio inputs into the computer has been a problem for most people. Either their system doesn't offer enough inputs, or the cost for purchasing more inputs is staggering. These problems are now history. The 24i delivers two dozen balanced 24-bit analog inputs in one rack space at a price that will make your jaw drop. And it's expandable to 72 inputs."

The 24i Core System and 24i Expansion I/O

The 24i core system includes a 24i single-rack space I/O, a cross-platform PCI-324 audio card, ASIO software drivers for Mac and PC, a multi-channel Wave driver for Windows 95/98, a Sound Manager driver for Mac OS, and MOTU's AudioDesk™ workstation software for Mac OS. AudioDesk includes sample-accurate editing, sample-accurate sync, 24-bit recording, 32-bit native effects processing, a wide range of 3rd party plug-in support, editing, mixing, processing and mastering.

The 24i expander consists of a single rack-space 24i unit, which can be added to a core 2408, 1224 or 24i system for an additional 24 balanced analog inputs.


A 24i core system includes the same expansion-ready PCI-324 audio card introduced with MOTU's popular 2408 hard disk recording system. Users can connect up to three audio interfaces to the PCI-324, mixing and matching 24i, 2408, 1224 and 308 rack I/Os to suite their needs. For example, up to three 24i audio interfaces can be connected to a core system for as many as 72 simultaneous analog inputs.

Front and rear panels

The rear panel of the 24i, from left to right, has a power cord receptacle, vertically stacked BNC connectors for word clock in/out and 24 phone jack (TRS) inputs with 24-bit oversampling converters that measure a dynamic range of 111 dB. Above the inputs, on the right-hand side, are a pair of analog TRS main outs, accompanied by S/PDIF digital main outs supplied in two formats: optical (TOSLink) and RCA (coax).

The front panel of the 24i six-segment level meters for each of the twenty four inputs, along with sample rate indicators (44.1 or 48 kHz). Six segment stereo meters are also provided for the main outs. Finally, a stereo quarter-inch headphone jack with volume knob is also provided.


For synchronization, the 24i provides word clock input and output on standard BNC connectors. It can be clocked from the PCI-324 card, a 2408 or 1224 interface connected to the card, or from its own word clock input.

AudioDesk Audio Workstation Software for Mac OS

The 24i core system includes AudioDesk, a full-featured audio workstation software package that includes 24-bit recording, multi-channel waveform editing, automated virtual mixing, graphic editing of ramp automation, real-time effects plug-ins with 32-bit floating point processing, crossfades, support for third-party audio plug-ins (in the MOTU Audio System and Adobe Premiere formats), background processing of file-based operations, sample-accurate editing and placement of audio, and more. The 24i system can also be used with MOTU’s award-winning Digital Performer audio sequencer software package.

In either case, the host computer determines the number of tracks that the software can record and play simultaneously, as well as the amount of real-time effects processing it can support. A faster computer with more RAM and faster hard drives will allow more simultaneous tracks and real-time effects than a slower computer with less RAM and slower hard drives. A 300+ MHz Power Macintosh will allow the software to play 24-32 simultaneous tracks of audio. Today's fastest Macintosh computers can typically play as many as 64 tracks or more. Standard third-party SCSI acceleration products can also help users achieve higher track counts.

Drivers for Compatibility with Third-Party Audio Software

The 24i system ships with a standard multi-channel ASIO driver for Mac OS and Windows, allowing users to record, edit, play back and mix their 24i projects using their favorite ASIO-compatible audio software. Similarly, a Wave (.WAV) driver is also provided for compatibility with any Windows audio software that supports standard, multi-channel Windows Wave drivers. Also included is a standard Mac OS Sound Manager driver for stereo I/O with any audio application that supports Sound Manager.

MOTU is now shipping the 24i. Price is $1195 for a 24i expander and $1495 for a 24i core system.

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