The Fundamentals of Digital Signal Processing in Sound Reinforcement Systems 

Contributors: Jim Brown and Gino Sigismondi

Key Takeaways

• Digital signal processing (DSP) converts analog audio into digital data that can be analyzed and optimized, helping improve sound quality in theaters, auditoriums, and houses of worship.
• Modern digital signal processors combine multiple audio tools into a single platform, including equalization, dynamics processing, delay, feedback reduction, and automatic microphone mixing.
• DSP can help address common sound reinforcement challenges such as feedback, poor intelligibility, inconsistent signal levels, and unwanted noise.
• While DSP is a powerful audio tool, it cannot replace good acoustic design and sound system fundamentals, making proper microphone, loudspeaker, and room design equally important.
• Professional audio engineers rely on DSP for greater flexibility, control, scalability, and system optimization, making it a core technology in modern audio systems.

You've done everything you can think of to keep the levels constant.  You've added amps.  You've moved speakers.  Still, the amount of reverberation in your worship space makes intelligibility a real challenge. Then, of course, there's background noise and feedback.  Believe it or not, there may be a simple solution to combating these sound quality issues.: digital signal processing (DSP). 

Whether audience members are in a theater, an auditorium, or a church like yours, they have high expectations about sound quality. Digital signal processors can play an important role in optimizing audio performance, improving intelligibility, and helping audio systems overcome common acoustic challenges. 

In this article, we'll explore the fundamentals of digital signal processing, including: 

• DSP – What is Digital Signal Processing?
• Signs and Symptoms: When Can DSP Help?
• Types of DSPs
• Practical DSP Applications

Shure's Gino Sigismondi explains what digital signal processors can—and can't—do, while audio expert Jim Brown of Audio Systems Group shares insights from real-world system design and deployment. 

How Digital Signal Processing Works

Digital Signal Processing converts signals from real-world sources (typically analog signals) into digital data that can then be analyzed and processed.  

Once a signal has been converted into digital form, a digital signal processor can isolate and manipulate specific components with a level of precision that is difficult to achieve in the analog domain.

When the DSP has finished its work, the digital data can be turned back into an analog signal with improved quality. A DSP can be used to reduce noise, amplify specific frequencies, suppress others, and improve overall audio quality. 

Types of Audio Signal Processors

Signal processors can be analog or digital, single- or multi-function, and may operate as standalone devices or as part of a larger audio system.

Most early signal processors were standalone devices, but over time, became multi-functional with today's digital signal processors (DSPs) combining a wide spectrum of functions at a fraction of the cost of individual processors. 

Common DSP Function
Today’s DSPs can include features such as:

• Volume and Gain Control
• Filters
• Equalization (EQ)
• Dynamics Processor
• Compressors
• Limiters
• Expanders and Noise Gates
• Automatic Gain Control (Speech Leveler)
• Delay
• Automatic Microphone Mixers
• Gated Automatic Mixers
• Feedback Reducers
• Acoustic Echo Cancellers

Digital signal processing is highly sophisticated technology, but it is also extremely common. DSP chips can be found in sound cards, cellular phones, modems, hard drives, digital televisions, and countless other devices.

According to Texas Instruments, DSPs are used as the engine in 70% of the world's digital cellular phones, and with the increase in wireless applications, this number will only increase.  

Beyond audio applications, digital signal processing is used in fields including communications, imaging, biomedicine, radar, sonar, seismology, speech processing, and music processing. 

What DSP Can Do

To determine whether DSP can benefit your audio system, you need to consider some of the most common problems you face in sound reinforcement Assuming your room acoustics are reasonably well controlled, DSP can help address many common sound reinforcement issues.

The following table outlines several common audio problems and the DSP tools typically used to address them. 

And What DSP Can't Do

While digital signal processing (DSP) can solve many common audio problems, it is not a substitute for good sound system design and accepted sound reinforcement practices.

For example, DSP cannot eliminate excessive reverberation within a room. Once sound leaves a loudspeaker and interacts with the acoustic environment, signal processing can no longer control it. In these situations, simply raising the level of the sound system will only make the problem worse rather than improving intelligibility.

Best Practices for Sound System Performance

While digital signal processing can help address many audio challenges, good results still depend on proper sound system design and operation.

Consider the following best practices: 

• Keep unwanted sounds from entering open microphones by choosing microphones with the appropriate polar pattern.
• Turn off microphones that aren't in use.
• Keep microphones close to the sound source.
• Aim directional loudspeakers away from reflective surfaces and toward listeners.
• Reduce room reverberation through structural modifications or acoustic treatments.

An Expert's Perspective on Digital Signal Processing

Jim Brown, Audio Systems Group
To gain another perspective, we contacted Jim Brown, who is the founder and principal consultant for Audio Systems Group in Chicago. He has published numerous research papers on sound reinforcement and is a contributor to pro sound magazines, including Sound & Video Contractor and Technologies for Worship. 

He's designed hundreds of sound systems for a wide variety of installations and started using DSP in 1995.  Jim hasn't done a system without one since, and here's why:

Flexibility
"One piece of equipment, often taking up no more than one or two units of rack space, can fulfill my wildest dreams."

Expanded Processing Capabilities
"I can do a lot more signal processing that I could with separate analog gear.  There's no longer any excuse for not tuning the send to the ceiling loudspeakers and it's easy for me to delay them so that they don't create an intelligibility problem."

Programming Ease
"For instance, the user interface for an equalizer looks and feels just like the controls of the analog unit it replaces.  I have a real time display of the equalizer's response as I tune it.  The compressors and limiters give me control of all the setup parameters, showing gain reduction dynamically with signal."

Documentation and Backup
"I can save the file to my laptop when I'm done.  I can also save different variations."

Portability
"I can work through a design in my office, understand the free DSP and I/O available for expansion of the system – all without the need to have any contact with the hardware itself."

Scalability
"Things like "Oh, by the way, you know we need to feed the system from the portable baptismal font that we set up at the back of the church, don't you?" are easily accommodated."

Pre-sets
"I can create customized pre-sets and call them up with external control signals in the form of switched contacts, logic signals and user control screens.  This is perfect for churches with a variety of worship services and programs."

Reduced Noise in the Signal Chain
"Before DSP, we had to worry about the cascading of noise contributed by each and every analog input and output stage."

Simplified Installation
"With DSP, all we have to do is connect inputs and outputs.  The rest of the wiring all happens on the computer screen."

Cost
"Installation costs are minimal and hardware costs are much less, too. If we add the costs of a compressor/limiter, equalizer, crossover and delay, we're even with the cost of a simple DSP that replaces them.   Since the DSP can be used anywhere, the more applications you can find for it, the more you save."

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Additional DSP Resources

For additional information on digital signal processing, audio system design, and signal processor selection, explore Selection and Operation of Audio Signal Processors

And if you'd like to learn more about Jim Brown, and the range of his talents, which extend from producing NPR's "Jazz Alive!" to his 4 1/2 star review in Downbeat for his "Carmen McRae at Ratso's" CD visit Audio Systems Group.

FAQ: Digital Signal Processing (DSP) 

What is digital signal processing (DSP)? Digital signal processing (DSP) is the process of converting real-world signals into digital data so they can be analyzed and manipulated before being converted back into usable audio.

How does a digital signal processor improve audio quality? A DSP can help optimize audio by reducing noise, adjusting frequency response, controlling signal levels, and applying processing such as equalization, delay, and feedback reduction.

What types of problems can DSP help solve? DSP can help address common sound reinforcement challenges including feedback, poor intelligibility, inconsistent signal levels, unwanted noise, and loudspeaker alignment issues.

Can DSP fix poor room acoustics? No. DSP is not a substitute for good acoustic design. Problems such as excessive reverberation must be addressed through room treatments, structural changes, or other sound system best practices.

What functions are commonly included in a DSP? Modern DSPs often combine multiple processing tools in a single device, including equalization, dynamics processing, delay, automatic microphone mixing, feedback reduction, and acoustic echo cancellation.

Why do audio professionals rely on DSP? DSP provides flexibility, scalability, simplified system design, and the ability to perform multiple signal processing functions within a single platform, making it a valuable tool in modern audio systems.