ST Audio DSP2000 C-Port Recording Interface

The DSP2000 C-Port recording system is a combination of ST Audio's Audio DSP24 PCI card, XG-DB1 daughterboard, and ADC&DAC2000 converter box. The Audio

The DSP2000 C-Port recording system is a combination of ST Audio's Audio DSP24 PCI card, XG-DB1 daughterboard, and ADC&DAC2000 converter box. The Audio DSP24 card uses the IC Ensemble Envy24 I/O digital signal-processing chip and supports ten channels (eight analog and two digital) of full-duplex 24-bit, 96 kHz recording. Four DSP24 cards can be linked with sample-level accuracy for a total of 40 channels.

The ST Audio DSP24 card provides ⅛-inch stereo line inputs and outputs, an ⅛-inch mic input, and two internal aux/CD inputs. S/PDIF optical and coaxial stereo I/O and AES/EBU I/O are provided through a daughterboard that connects to the card with a small cable and mounts in a PC's case slot without plugging in to the PCI bus. The AES/EBU connections use ⅛-inch TRS minijacks; no adapters to XLR connectors are supplied.

A 44-pin connector on the DSP24 card provides an interface that can accommodate a number of specialty external ST Audio boxes to provide multichannel A/D/A conversion and ADAT and TDIF inputs and outputs. The ADC&DAC2000 converter box connects through this port.

The ADC&DAC2000 is an attractively finished, dark blue brushed-metal 1U rackmount box that houses the unit's AKM 4524 converters, keeping them away from the electrically noisy environment inside the computer case. The unit provides eight unbalanced ¼-inch inputs and outputs, a ¼-inch headphone output with volume control, and a single stereo input/output pair with XLR3 connectors. The XLR3 inputs feature gain controls as well as switchable 48V phantom power. The ADC&DAC2000 also provides one MIDI In and two MIDI Outs.

The 6-foot cable that carries data from the PCI card to the box and supplies power from the CPU is long enough for most applications. I did not see a longer cable offered as an option, should it be required.

The outputs of the ADC&DAC2000 are referenced to -10 dBu rather than the +4 dBu professional standard, which means the unit will be headroom-shy in a professional-equipment environment. That and the unbalanced outputs are doubtless the results of efforts to keep the price of the system low. On the other hand, ST Audio does make costlier external converter boxes that have balanced inputs and outputs.


The DSP2000 C-Port's software was easy to install on my Windows ME system, a Celeron processor with 512 MB of RAM. Windows driver software is included in the package, and third-party drivers are available for Linux and BeOS.

Signal flow, driver settings, and other hardware settings are controlled by an included application called External Links. Fig. 1 shows the Main External Links window, a virtual patch bay, where the right-to-left signal routing is managed with colored patch cords.

The External Links patch bay is divided into three main sections. Available inputs are shown at the window's right. In Fig. 1, the metallic-gray rectangle represents the ADC&DAC2000 external box with its four pairs of audio and MIDI inputs. The ADC&DAC2000 box was chosen from External Links' Add Inputs menu. Immediately below the ADC&DAC2000, the XG daughterboard appears as a choice for S/PDIF or AES/EBU input.

The middle section of the window (in green) shows the DSP24 card's input/output resources. The gray connectors on the right represent the card's input channels, and the white connectors on the left represent outputs. The gray panel marked DAC at the far left of the screen is where “virtual” outputs are routed to the card's actual output channels.

The labeling of the various virtual jacks on the patch bay is not intuitive. At first I was confused by the screen, especially by the middle section of the interface.

In addition to the External Links Patcher, the control software includes an Internal Mixer that manages settings for routing signals to and from jacks and internal inputs on the DSP24 PCI card. A software External Mixer lets you control settings on the ADC&DAC2000 box. With all tracks active, the External Mixer application takes up too much screen area, but it cannot be resized. The meters are a bit sluggish, making monitoring difficult. Both mixers can be started from the External Links file menu.

The DSP2000 C-Port system feature I enjoyed most was the ease with which I was able to control signal monitoring. It's possible to monitor each stereo channel pair directly and without any latency by connecting inputs on the middle section of the virtual mixer to outputs on the left section. You might use that, for example, to send out monitor signals of a microphone connected to Input 1/2 to the headphones of a performer (connected to the headphone output of the external box).


The DSP2000 C-Port distinguishes itself greatly in its ability to route audio to different drivers simultaneously. The unit supports MME, ASIO 2.0, and GSIF (Giga), and it was simple to run Tascam GigaStudio with its GSIF drivers simultaneously with Steinberg Nuendo and Emagic Logic Audio running ASIO 2.0 drivers. You assign drivers in the External Links Hardware Settings window. Latency in the system can be as low as 2 ms.

I tested the unit with a variety of Windows software, and in general, the unit performed beautifully. There were some initial problems with the computer locking up when I used GigaStudio 2.0, but the trouble vanished when I upgraded to version 2.5. The DSP2000 C-Port system is bundled with Emagic Logic SoundTrack 24. It's preconfigured for the C-Port and capable of 16 tracks of audio at a resolution of 24-bit, 96 kHz.

ST Audio's printed manual is adequate, though the section on software control leaves a lot to the imagination. The ST Audio Web site, however, is another story. Besides offering tech support, the site is full of useful information and includes FAQs, a knowledge base, and documentation of users' experiences with the unit. For the most part, the experiences appear to be good, though, to its credit, ST Audio is not afraid to publish comments from disgruntled customers. I was pleasantly surprised at the responsiveness of the tech people: turnaround times were quick, and the techs knew their stuff.

The C-Port is certainly one of the best digital-audio interface values today. The unit is nicely expandable to include options such as ADAT and T/DIF I/O and balanced inputs and outputs. Sound quality is superb: quiet, with clear highs and quick transients that are especially noticeable and appreciated in high-end drum samples. The unit is selling like hotcakes in Europe, and I wouldn't be surprised to see this product quickly become one of the most popular audio systems in the Windows music world.

Thomas Wellshas been involved in computer music for more than 25 years. He teaches at Ohio State University.

Minimum System Requirements

DSP2000 C-Port
Pentium/133; 32 MB RAM;
Windows 95/98/ME/XP/NT/2000


ST Audio
DSP2000 C-Port (Win)
digital-audio interface


PROS: Excellent value.

CONS: No balanced outputs.


ST Audio

DSP2000 C-Port Specifications

ADC&DAC2000 External Converter Unit

Analog Inputs(8) unbalanced ¼" (-10 dBu);
(2) XLR3 (-24 to +50 dB) with switchable phantom power (48V)Analog Outputs(8) unbalanced ¼" (-10 dBu); (2) balanced ¼" (-10 dBu)A/D Converters24-bit, 64× oversamplingD/A Converters24-bit, 128× oversamplingSampling Rates22.05-96.00 kHzOther Ports(1) MIDI In; (2) MIDI Out; (1) ¼" TRS stereo headphoneDimensions1U × 5.75" (D)Weight3.3 lb.
DSP24 PCI Host Card with XG-DB1 Daughterboard

Analog Line Inputs(1) unbalanced ⅛" (-10 dBu)Analog Mic Inputs(1) unbalanced ⅛" (-24 to +50 dB)Analog Line Outputs(1) unbalanced ⅛" (-10 dBu)Digital I/O(1) optical in (S/PDIF); (1) RCA coaxial in (S/PDIF);
(1) optical out (S/PDIF); (1) RCA coaxial out (S/PDIF);
(1) AES/EBU in ⅛"; (1) AES/EBU out ⅛"A/D Converters24-bit, 64× oversamplingD/A Converters24-bit, 128× oversamplingSampling Rates22.05-96.00 kHz