What is digital signal processing?
DSP has long been an essential part of music production, even with the periodic revival of analog technology, DSP will continue to be an integral part of the studio recording and music production experience. Hence having a strong understanding on the concept of DSP should be a part of your music production knowledge.
Digital signal processing (DSP) refers to the manipulation of different types of signals in order to filter, compress, measure, or produce analog signals. As it applies to music production, DSP processes audio signals in digital form and manipulates the signal via various mathematical processes.
The most common applications of DSP in the music production world include improving the quality of the signal, reducing noise, compensating for excessively high–or excessively low–volume levels, and modifying the signal via equalization or some other process.
Origins of DSP
The origins of DSP go back to the earliest days of digital computers in the 1960s and 1970s. With computer technology still in its infancy, very few people had access to the hardware and software necessary to perform DSP-related tasks. Most DSP applications at the time therefore revolved around areas such as national security, oil exploration, the space program, and medical imaging.
The advent of more affordable technology in the 1980s and the 1990s brought about a computer revolution of sorts, and more people suddenly had access to (relatively) powerful personal computers. Around the same time, DSP began expanding outside the military and medical spheres, and exploration into its commercial potential began in earnest. Initially seen in devices such as mobile phones, CD players, and the like, DSP was soon utilized in a host of audio processing devices and systems.
Analog vs DSP
Analog signal processing and digital signal processing both have their pro and cons. On the one hand, the use of discrete components in an analog signal processor means that the circuitry is easier to assemble, easier to diagnose and repair, and is less costly overall.
In contrast, the use of integrated circuits (ICs) in a typical DSP processor makes repair–and even replacement–extremely difficult, if not totally impossible. Generally speaking, an analog signal processor can be easily modified and repaired if necessary. With DSP devices, modification is next to impossible, and replacement is the only option if it breaks down.
DSP units also generally result in a much cleaner and noise-free signal than their analog counterparts. This is often preferable in situations where signal clarity is a priority.
However, the warmth, distortion, and perceived “fuzziness” of analog signals aren’t necessarily undesirable qualities. For more creative applications where having a distinctly vintage ‘vibe’ is needed, an analog signal processor might actually be preferable to a DSP unit.
Pros and Cons of DSP
DSP offers a number of important advantages in a music production context.
Many DSP devices pack much more functionality into smaller form factors than their analog equivalents. This makes it possible to perform a multitude tasks with fewer and smaller pieces of equipment than was previously possible.
Cutting down on the equipment necessary to do a particular job also reduces clutter and connectivity concerns. Less equipment also means that there are fewer things that can go wrong, and fewer things that can break down and require repair or replacement.
Programming
The ease with which DSP devices can be programmed is a key advantage that many musicians and producers routinely make use of.
Equalizers for example can be programmed to a remarkably precise degree, and they can even provide real-time feedback on how the signal is being affected. Real-time visual feedback is especially important with devices such as compressors and limiters, with which the effect on the sound isn’t always readily apparent.
The list of advantages of DSP goes on and on. In fact, it is safe to say that its advantages far outweigh its disadvantages.
One of the few criticisms that can be levied against DSP as compared to analog processing is that the precise nature of the digital technology sometimes results in an overly clean and sterile sound. In this case, often another DSP device like a tape saturation emulation plugin, or an hardware unit like an analog summing mixer is brought in to make things sound more natural.
In most cases, however, this precision and clarity is totally desirable, and they are in fact some of DSP’s biggest strengths. But in the oftentimes-subjective world of music production, where perceived flaws and imperfections often contribute to a ‘vibe’ or a creatively distinctive result, the perfection imparted by digital circuitry may not necessarily be the right fit.
Technology
As far as the technology itself goes, DSP typically requires significantly more bandwidth than analog equivalents. This need for high bandwidth devices and circuitry often translates into higher costs.
Working with digital signals also require synchronization between various devices, which means that any investment or purchase decisions will have to be made with consideration to the overall integration of the various components.
Types of DSP
DSP-capable devices come in many forms.
In a typical music production setup, most devices perform multiple functions. That being said, there are still certain pieces of specialized equipment that perform only one or two specific tasks, such as feedback elimination or digital-to-audio (DA) conversion (Wiki article).
Other specialized pieces of DSP equipment perform functions such as filtering, noise reduction, audio enhancement, and signal editing.
Many DSP-equipped effects processors are capable of multiple functions, often at the same time. While some devices may specialize primarily in reverb, delay, or compression effects, others may perform two or more of these functions by way of multi-effect signal chains.
These are some of the different tasks that DSP devices are typically called upon to perform in a music production setting:
- Volume and gain control
- Filtering
- Equalization
- Dynamics processing (compression, limiting)
- Noise gating
- Expansion
- Delay, reverb, modulation effects
- Feedback elimination/reduction
How DSP is Utilized in Audio Production
One of the most common uses for DSP in a recording studio is applying effects to audio signals. As mentioned already, DSP effects processors can perform a multitude of effects-related tasks from applying delay, reverb, and modulation effects to reducing dynamics, improving audio clarity, and so on.
The more astute among you will notice that some of these functions can be performed just as easily–and perhaps even more so–within a computer.
The question that arises then is “Why is there still a need for dedicated DSP devices?” Particularly a device such as an audio interface, mixer, hardware reverb unit.
DSP in Hardware
One of the most important things to realize about signal processing is that every single task or function adds to the load taken on by the computer’s CPU. Every EQ plug-in, every reverb, every compressor…all of these add to the total resource utilization of your computer. Even the most powerful CPUs have their limits, and you will run into them eventually the more plug-ins you add to the mix.
External DSP devices take some of the load off your computer’s CPU, leaving more resources available for mixing, managing the various bits of audio, and running the operating system.
With judicious use of a DSP unit as part of an integrated recording system, you will reduce the overall load on your computer and possibly avoid pushing your CPU utilization meter into the red.
Example Hardware Devices that Use DSP
We’ve already explained how DSP-equipped devices can take some of the load off your computer’s CPU. Apart from dedicated signal processors, devices such as audio interfaces and mixers can provide similar benefits by incorporating digital signal processing into their base sets of functionalities.
The Steinberg UR28M is a good example. A state-of-the-art audio interface that could easily fulfill the bulk of your I/O requirements, it also has onboard DSP capabilities. This device enables you to perform zero-latency foldback monitoring, while treating audio signals with its own EQ, reverb, and dynamics processing effects.
Another audio interface, the Universal Audio Apollo Twin MKII includes a bundle of high-quality processor plug-ins such as Teletronix LA‑2A and 1176 compressors, Pultec EQs, and the 610‑B Preamp. A totally capable, professional-grade audio interface in its own right, the Apollo Twin MkII can take a hefty load off your CPU, while at the same time improving your mix with some truly world-class plugins.
The Apogee Ensemble Thunderbolt is another audio interface that combines outstanding audio quality with onboard DSP capabilities. With a host of cutting-edge features and functionalities, the Ensemble Thunderbolt is ideally suited for re-amping guitar tracks.
Mixers such as the Allen & Heath ZED-10FX and the Alesis MultiMix 8 USB FX also come with DSP capabilities. In addition to performing their primary functions as mixers, they could also be used as auxiliary effects devices.
Final Thoughts
DSP has long been an essential part of music production. Even with the periodic revival of analog technology, DSP will undoubtedly continue to be an integral part of the studio recording and music production experience.
