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The SSL Duende is a DSP plug-in host that connects to your computer via FireWire.

Although founded to make solid-state control systems for pipe organs, Solid State Logic (SSL) became widely known for its 4000-series large-format mixing consoles in the late '70s. As the first consoles to include dynamics processing on every channel, and boasting a pioneering automation system, the 4000-series became a studio standard, familiar both sonically and operationally to legions of engineers (myself included).

A great many SSL products have been built on the legacy of the 4000-series. The Duende DSP host is one of these products, though its technology was actually lifted from the company's C200 digital production console.

As the market for large-format music mixing consoles has waned, SSL has branched out into broadcast and postproduction consoles and, most recently, the project studio market. The Duende is intended to bring the famous sound and features of an SSL 4000-series channel strip within reach of the project studio market, and it does so quite well.

Thinking Outside the Box

In order to run the C-series algorithms, the Duende appears in a digital audio sequencer as if it were a software plug-in, following the recent trend of hardware DSP hosts such as the Waves APA, the TC Electronic PowerCore, and the Universal Audio UAD-1 card. The Duende is a 1U device that communicates with a computer over a FireWire 400 port. It supports VST, AU, and RTAS plug-in formats, at sampling rates up to 96 kHz. The front panel has only an AC power switch, while the back panel has two FireWire ports and an input for DC power from the wall-wart power supply.

Because the Duende takes care of the 40-bit floating-point digital signal processing, the minimum system requirements for the host system are not steep: a 1 GHz Pentium 4 or AMD computer running Windows XP SP2, or a 933 MHz Macintosh G4 running Mac OS X 10.4.8. The Duende needs 80 MB of hard-drive space.

Although the device goes easy on your CPU, it takes its toll on the FireWire bus. SSL recommends dedicating a FireWire bus to the Duende, but I say it's a necessity. Note that many computers have multiple built-in FireWire ports that often are all on the same bus, so it is likely you will need to add a FireWire card, which is not expensive but does take up one of the slots in your computer. In certain situations, there can also be some pesky interactions between the Duende and your other computer hardware (more on this later).

A Fine Pair

The Duende comes with only two plug-ins: Channel and Bus Compressor. SSL plans to develop and release additional plug-ins in the future, the first being the DrumStrip drum processor ($299), which should be available by the time you read this.

FIG. 1: Channel''s basic settings are very easy to grasp, and a variety of internal routing options are available.

Channel re-creates the classic SSL 4000 channel strip, with a 4-band equalizer, highpass and lowpass filters, a compressor, and an expander/gate (see Fig. 1). (SSL says the EQ and dynamics are taken from the XL 9000 K-series console, but it sure looks like the 4000 to me.) Bus Compressor is modeled after the 4000-series master bus compressor, renowned as one of those audio devices that just make things sound better coming out than they sounded going in (see Fig. 2).

Both the EQ and the dynamics in the Channel plug-in have a few tricks up their sleeve, nearly all of which are based on the original channel strip. The EQ has two parametric bands and two bands of shelving EQ, but the Bell button on the shelving bands makes them into peaking filters. The 4000 consoles had two primary incarnations: the E- and the G-series. One difference between them was that the E-series EQ had no overshoot, making it more surgical, whereas the G-series had overshoot and undershoot that made it more musical, if less precise. The E button in the Duende plug-in's interface allows you to switch between these two response types — a very nice touch.

FIG. 2: Bus Compressor is -modeled on the 4000 console''s master bus compressor, famed for its ability to pull together mix elements.

The control paths, or sidechains, of Channel's compressor/limiter and expander/gate are in parallel, with the two control signals applied to a single gain element, which presents some interesting processing possibilities. The compressor/limiter has switch-selectable peak or RMS detection, and both parts of the dynamics section have autosensing attack times.

Channel offers an almost complete matrix of routing options: filters before or after EQ, dynamics before or after EQ, filters and/or EQ in the dynamics sidechain, and so forth. Input and output level controls and an input polarity reverse switch complete the module.

The plug-in's interface replicates the 4000's layout and look, which unfortunately is as constraining as it is understandable. For example, Channel reproduces the 4000's 6-LED ladder meters, which were always just a bit better than nothing at all, rather than taking advantage of the computer's graphics capability to show more-informative meters.

Bus Compressor is a totally straightforward compressor, although with stepped attack, release, and ratio controls, and with only three ratios to choose from (2:1, 4:1, and 20:1). It also has an interface that replicates the original, providing a familiar look that is of dubious ergonomics in the digital realm. In the case of Bus Compressor, the issue is the stepped switches, which are changed by clicking-and-dragging — an unnatural and imprecise method.

Both Channel and Bus Compressor can be instantiated as mono or stereo plug-ins. The Duende supports up to 32 instantiations.

Click here to read more of the Solid State Logic Duende article.

Speed Bumps

Getting the Duende operational was not as easy as I would have liked, though I couldn't call it a nightmare. When I received the device, Intel Mac support was just being released. This required me to update both the firmware for the processing module and the software that runs inside MOTU Digital Performer (DP), my digital audio sequencer. The updates had to be performed in the right order, but at first the Duende seemed reluctant to execute them properly. After a few attempts, I finally got both updates done (firmware 1.15 and driver version 1.24) and started to work with the Duende inside DP.

I quickly realized I could not keep my FireWire drives running while the Duende was online, because I do not have a FireWire card and my 3 GHz quad-core Mac Pro Intel Xeon machine has only one FireWire bus for the four ports on it. For a while, I kept the Duende window open all the time as I explored the product's features. When I finally closed the Duende window, DP started stuttering horribly. This was an entirely consistent problem. It took a few exchanges with SSL technical support (which was quite prompt, pleasant, and professional in our email exchanges) before I understood that the problem could be remedied by selecting Always Run In Real Time from the contextual menu in the plug-in window. I'd never seen this command in DP before. It is designed to allow prerendering for DSP-intensive plug-ins, which isn't possible with external DSP hardware.

Selecting that command fixed the problem. But every time I instantiated a Duende plug-in, I had to remember to select Always Run In Real Time or else I'd suffer the consequences. SSL says that this problem is unique to DP and does not occur with any other host.

Even after I made the proper menu selection, several times DP went into an odd mode where tracks played back out of sync. Deinstantiating a Duende plug-in seemed to fix the problem; I would then reinstantiate the plug-in and everything would play okay. I suspect (but can't prove) that this is related to communication glitches between DP and the Duende.

The Sweet Sound of Success

Having more or less tamed all the beasts, I got down to working with the Duende and enjoyed myself quite a bit. While I'd always found the 4000 E-series EQ serviceable (I've had little experience with the G-series EQ), it had never flipped my wig. I found the Duende's G-series EQ much more engaging than the E-series, and I started using it extensively (see Web Clips 1 through 3).

I found myself reaching for Channel often, even when I already had other plug-ins on a track. It didn't meet every need — sometimes I needed more bands of EQ or a different compressor characteristic, for instance — but Channel frequently made me very happy. I liked the EQ, especially in the low end, and the compressor usually worked well to tame dynamics problems. It was also very nice to be able to instantiate Channel in stereo, which you could not do on the 4000 consoles.

Bus Compressor, on the other hand, is magic. It's not a gain maximizer, it's not quite a leveler, and it's not really transparent. In fact, it combines a bit of each of these features to create an effect that pulls together all of the mix elements and makes them sit together well (see Web Clips 4 and 5).

The great part of having it as a plug-in was that I didn't just use it across the stereo bus; I often used it on individual tracks. It did a beautiful job of combining several background vocals into one creamy layer. Bus Compressor also made a crunchy electric guitar track feel like the instrument had been really loud when it was recorded. On bass, it just smoothed out the peaky notes. There are many different kinds of compressor sounds, and no compressor works for everything, but Bus Compressor is a very valuable tool to have for a variety of applications.

I often use more than one compressor on a track that really needs dynamics management, and I was interested to note that both Channel and Bus Compressor worked excellently in that situation. Again, you can't throw any two compressors on a track and get that well-managed sound without lots of pumping, but the Duende's compressors seemed to play well with others nearly all the time.

Although you can save your plug-in settings as presets, no presets are included with the Duende. Granted, the EQ and dynamics processing are pretty straightforward and not too hard to set up, but it would be helpful to have some of the classic sounds as jumping-off points.

SSL Authenticity

At $1,995, the Duende is at the high end of DSP hosts, especially when you consider that it includes only two plug-ins. On the other hand, Channel has a lot of functionality, both plug-ins sound great, and 32 instantiations is about what you would have gotten on a 4000 console, and more than you can get out of some other plug-in hosts.

Although the price of entry may be daunting to some, for those who really want the sound of an SSL console's dynamics and EQ, the Duende is the most affordable way to get it. Keep in mind that you will need to add a FireWire bus (unless you have a machine that actually has more than one bus and can afford to dedicate it to the Duende). But the result will be a classic flavor with which to season your music.

Larry the O is finally ready to throw away his 8-inch floppy disks of SSL automation sessions.


5 = Amazing; as good as it gets with current technology

4 = Clearly above average; very desirable

3 = Good; meets expectations

2 = Somewhat disappointing but usable

1 = Unacceptably flawed

DSP host and plug-ins



PROS: Famous SSL sound, including both E- and G-series EQ. Up to 32 instantiations. Plug-in setup is straightforward.

CONS: Only two plug-ins. Needs dedicated FireWire bus. Some problematic interactions when Digital Performer is host. No factory presets.


Solid State Logic

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