DSP

If you use any type of digital audio device — a computer, a workstation synthesizer, or even a humble CD player — you’re using DSP. The letters stand for “digital signal processing.” DSP is a generic term, not a specific technology. Synthesis, sampling, reverb, EQ, and more — it’s all DSP.

The details of how DSP works matter mainly to software engineers. For musicians, the big question is, “Do I have enough DSP horsepower?” The answer, as Dickens wrote in Oliver Twist, is usually, “Please, sir — can I have some more?”

Digital synthesizers have been around since the mid-1970s. But the early models were unbelievably primitive by today’s standards. As computer chips have gotten faster, it has become practical to do more and more with DSP. Until ten or twelve years ago, desktop computers weren’t fast enough to do any type of audio recording, much less generate synthesized tones. Today, computers are blazingly fast, and many musicians rely entirely on their computer’s CPU to supply the DSP. But we still crave more.

MEASURING DSP

The faster your computer’s CPU is, the more DSP power you’ll have. But it’s almost impossible to gauge the real muscle of a computer by looking at the numbers. My Pentium PC has a 3GHz Pentium processor, but it has less DSP than new dual-core CPUs that run at only 2GHz. Having a dual-core CPU is sort of like having two CPUs side by side. A correctly written program can take advantage of the dual CPU to provide more DSP — more mixer channels, more effects, and more synthesizer voices.

A more significant factor, though, is how efficient the software is. One software synth might be able to produce 100 notes at a time on my computer, while another synth would choke when asked to play six notes.

Most DAWs provide a CPU meter, which gives you a rough gauge of how much DSP power you’re using. In Windows, the Task Manager can generate a graph of CPU usage (see Figure 1).

If your computer runs out of steam when asked to produce a lot of voices, you can (in most DAWs) freeze some of the tracks, thereby freeing up CPU resources to do other types of DSP. But when a track is frozen, the workflow is interrupted. Unfreezing tracks, editing them, and then freezing them again is a big hassle. Adding more DSP will make your life much more pleasant.

ADD-ON HARDWARE SOLUTIONS

Buying a faster computer is one way to add DSP. But it’s often more cost-effective (and less of a headache) to add specialized music hardware instead. You can beef up your system with a separate hardware module, or add a circuit board that plugs into a slot inside the computer.

If your music computer is a laptop, external hardware is your only option. A module such as the Roland Sonic Cell connects to the computer with a USB or FireWire cable. It adds synth voices to your studio productions while adding no load to your computer’s CPU. Many modules of this type also provide high-speed, high-quality digital audio I/O for the computer, plus MIDI in and out jacks. They may also have features that allow you to detach them from the computer and use them at gigs.

Mac and PC owners with desktop machines can take advantage of DSP boards such as the Universal Audio UAD-1 and the TC Electronic PowerCore; laptop owners can use external versions of these same DSP engines. These solutions are designed to integrate seamlessly with your software. In addition to the hardware DSP, this type of product typically includes a software bundle with high-quality effects. Third-party software written specifically for these DSP boards can extend the power of your music computer still further.

High-end systems such as Digidesign Pro Tools HD utilize both a board that sits in the computer and a separate hardware module that provides multiple inputs and outputs for your audio connections. Pro Tools compatible audio processing plug-ins, written in the TDM format, are available from a number of companies.

JARGON JOCKEY

• CPU: The computer’s Central Processing Unit — the main chip that does the heavy lifting.
• DAW: Digital audio workstation. Technically, a workstation synth such as a Yamaha Motif or Korg M3 qualifies as a DAW, but the term is usually reserved for software. DAW programs like Pro Tools, Cubase, Sonar, and Logic provide audio recording, MIDI sequencing, and hosting for plug-in synths and effects.
• GigaHertz (GHz): A unit that indicates how fast the CPU works. The word “Hertz” is a fancy way of saying “cycles per second,” and “giga” means “billion,” so a 3GHz CPU can perform three billion operations per second.
• Track freeze:  A function that renders a track (usually a software synthesizer) to the hard drive as audio. The synth is then disabled, and the rendered file is played instead. Playing a digital audio file uses much less DSP than generating synth voices in real time.