What is DSP (Digital Signal Processing) & Does It Matters?

DSP is short for Digital Signal Processing. It stands for the processing of audio signals with digital techniques. It uses mathematical algorithms to change, adjust, analyze, and modify audio signals.

The effects of DSP are equalization, compression of audio, effects processing, virtual surround sound and noise cancelling. It is an essential tool in modern audio.

What is DSP?

DSP (digital signal processing) is a process that runs in a microprocessor chip dedicated to analyzing, modifying, and synthesizing continuously supplied digital data.

It takes digital data and modifies it based on the manufacturer’s or user’s preference. It’s used for speech, audio, image, and video processing. It’s an essential part of our digital world.

In audio, you can use a wide variety of DSP functions:

• Audio corrections in wireless headphones (and room corrections for speakers)
• Graphic audio equalizers
• Surround sound features like Spatial Audio
• Active noise cancellation & noise reduction for calls
• Speech recognition
• Audio decoding & encoding
• Audio compression & decompression

Digital vs. analog signal processing

Both aim to do the same, but digital signal processing algorithms are more flexible in what it can do, and most importantly, it’s simpler and cheaper to implement.

Analog signal processing changes the sound by changing electrical flow through active and passive electrical components.

Digital signal processing uses chips like DSPs, FPGA, and ASIC that take digital data and tweak it by performing mathematical equations.

Example of DSP

Above, we glanced over most of the things DSP does for audio processing. Let’s look at how those things improve your user experience.

Audio effects processing

Upon decoding your music files, DSP can alter the output signal by adding audio effects or corrections. These effects are either added by you (the user) or the manufacturer.

User added effects

The most common user-added effect is EQ or equalization. If you boost bass or enable a virtual surround sound feature, DSP acknowledges that and process data accordingly.

Remember that the quality of these effects depends on the quality of instructions provided by the software you use.

Often, when boosting frequencies, you notice a significant drop in loudness or dynamic range, meaning that instructions from the app were poor.

Pick some apps from the How to increase bass article for the best listening experience.

Manufacturer added effects

All Bluetooth headphones use DSP to correct their sound in real-time.

• You can hear that something is off when you listen to Sony WH-1000XM4 in wired mode. Since only the left earcup has an auto play/pause sensor, the audio sounds different from the left channel. That’s because, in wired mode, headphones don’t use DSP to correct the tuning of the left channel.

Furthermore, DSP is used for Adaptive EQ, which constantly changes the tuning based on how you wear your headphones/earbuds.

Audio mixing and mastering

When recording audio, you want it to be as clear and neutral as possible, so you can later make adjustments to it, like correcting signal peaks and adding reverb, distortion, and other effects.

Just listen to almost any song in your playlist, and you’ll hear the echo in vocals, reverb in instruments, the sensation of soundstage, and instrument separation.

That’s all added afterward in the mixing and mastering stage. And to do that, the audio signal had to go through the DSP.

Active noise cancellation

DSP takes a digitalized signal from the microphones, process it according to software instructions, and ensures that the output signal has its phase inverted. Then the DAC converts it and plays it back into your ears.

While that sounds like a lot of work, it all happens in a split second. Otherwise, active noise cancelling simply wouldn’t work.

Voice recognition and enhancement

A digital signal processor is also used to activate and communicate with voice assistants or for a speech-to-text feature.

• DSP first detects the speech in the input data, dissects and analyses it, and then compares it to a pre-defined database to construct the sentence humans can understand.

Speech recognition and enhancements are also essential for processing voice during phone calls. 

Computers, mobile phones, or headset mics, use an algorithm to isolate your voice from the background noise, try to clear it up, and make it more intelligible.

Benefits of Using DSP

The main benefit of using DSP is that it enables a wide range of features at a relatively low cost compared to analog signal processing. It’s more flexible to use and easier to integrate.

So, what does DSP do? Most notably, it can correct the sound where it would otherwise be impossible or too expensive to fix.

Examples of correcting audio:

• User graphic EQ, where you can tweak specific frequencies to make the sound just how you like it.
• Adaptive EQ feature inside some Bluetooth headphones uses an internal mic that’s constantly analyzing the sound and making EQ changes in real time.
• More expensive AV receivers come with a microphone that measures your room frequency response and tweaks the audio to sound as the manufacturer intended.

In a nutshell, DSP is useful to squeeze the maximum from your equipment. And helps you achieve a better listening experience without you being an audio expert and making tweaks by yourself.

Furthermore, it also ensures that certain features like EQ, ANC, or virtual surround sound are more widely available to customers.

Disadvantages of using DSP

One of the main reasons why DSPs in audio earned a rather negative connotation is that they can ruin the immersion and dynamic range of some Bluetooth audio devices.

That is most obvious in Bluetooth speakers, where DSP dynamically adjusts the bass response and lowers audio peaks to protect against damaging the drivers.

However, the result is a muted sound that can sometimes drop in loudness in the middle of the song. Like when you expect a loud gunshot, but you barely hear it.

Remember that, in most cases (like in computers), DSP doesn’t tinker with your audio unless you explicitly order it.

How does DSP Work?

DSP changes digital signals by performing mathematical functions like “add”, “subtract”, “multiply”, and “divide”. It sits in the middle of the audio interface diagram:

1. Analog signal (captured by a microphone)
2. Pre-filter (that filters out unwanted frequencies below or above the human hearing threshold from captured analog signal)
3. ADC (analog-to-digital converter)
4. DSP (takes the digital signal and encodes it into or decodes it from a desired audio format like mp3 or FLAC)
5. DAC (digital-to-analog converter)
6. Post-filter (that filters unwanted frequencies generated by DAC)
7. Amp (to boost generated analog signal to normal listening levels)
8. Audio playback device (headphones or speakers playing sound)

DSP’s behavior is determined by software instructions made by you (tweaking the EQ, selecting in what codec to export your audio recording) or the manufacturer (tuning the Bluetooth headphones).

Digital signal processing techniques for audio

When you wish to play music from your device, digital signal processor decodes and applies changes to the digital data. Music studios are especially heavy users when it comes to DSP tweaking, as they can use:

• Equalization
• Compression
• Distortion
• Reverberation
• Modulation
• Saturation
• Chorus
• Flagellation

Signal encoding and compression

DSP encodes digital audio data into audio formats like mp3, FLAC, WAV, etc. That also means it is responsible for storing files lossless or lossy by eliminating redundant data.

Moreover, DSP compresses audio files to save storage on your device (don’t confuse that with dynamic range compression when you lower signal amplitudes).

Compression is the process where algorithms look for repeating data patterns and find different ways to “remember” them more efficiently.

For example, DCT compression is used to compress speech, whereas linear predictive coding (LPC) or modified discrete cosine transform (MDCT) is used for both speech and general audio.

That said, audio formats determine what compression method DSP has to use. Therefore, depending on the format, it also knows how to decompress the file.

Signal filtering and equalization

The most important job of DSP signal filtering is signal separation (eliminating or at least reducing unwanted noise) and signal restoration (correcting a distorted signal).

Meanwhile, equalization is when DSP changes the data so that DAC reconstructs specific frequencies with different amplitudes as it usually would. Therefore, some frequencies get louder or quieter, depending on how you equalize them.

DSP vs. CPU (what’s the difference?)

DSP is a specialized hardware designed to analyze and modify large quantities of digital data quickly. It is smaller and has a relatively low number of instructions to perform (quicker processing time).

In contrast, the CPU (central processing unit) is a general tool designed to communicate with every component in the system and ensure they all work together.

Frequently Asked Questions (FAQ)

Conclusion

You can find digital signal processors in almost all modern devices that deal with audio or video files. They help with their storage and decoding as well as modifying and compressing.

They play a vital role in audio, making EQ corrections, tweaking it so it sounds more “3D”, blocking outside noise with ANC, ensuring voice assistants can understand us, and many more.

Because of that, DSP is here to stay, with more and more devices relying on its powerful features.

Peter Susic

From a childhood fascination with sound, Peter’s passion has evolved into a relentless pursuit of the finest headphones. He’s an audio expert with over 5 years of experience in testing both audiophile and consumer-grade headphones. Quote: “After many years, I can confidently tell which headphones are good and which are terrible.” Find his honest opinion in his reviews.