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Digital signal processor buying guide

Optimize your car stereo sound with a DSP


any of our customers are appalled at the audio quality of their factory stereos and want to improve the sound, but can’t change out the radio because its controls are tied in with other essential systems.

A solution we like to recommend is to install an aftermarket amplifier and speakers, then add a digital signal processor (DSP) to dial in the sound. DSPs give you tons of control over the sound, and are essential for overcoming factory flaws.

Read on for an overview of how DSPs work and what features to look for when shopping.

signal flow diagram

How do you hook up a signal processor?

With a factory stereo, you’ll connect your factory speaker wires to the DSP’s inputs, then connect your DSP’s outputs to your amplifier using RCA patch cables. Some DSPs will even accept input signal from higher-power factory outboard amplifiers, which is sometimes necessary.

Aftermarket stereos can also benefit from a DSP, connected via RCA cables to the stereo’s preamp outputs.

AudioControl DM-608

What to look for in a signal processor

Shopping for a DSP can be confusing, especially if you're not already familiar with them. Below, we'll run through the most common features you'll find. Always make sure the DSP you're considering has everything you need. For example, not every DSP offers bass restoration.

So, here are the features and functions that you can expect to find in most digital signal processors.

DSP controls — knobs or software

Basically, there are two kinds of digital signal processors:

  • Those with onboard controls. This traditional style of control lets you easily tweak settings on the fly. On your way to work, you notice a crossover point that needs to be adjusted? No problem, take a minute and make the adjustment when you get to work.

    The downside is that the DSP needs to be accessible. You probably wouldn't want to mount one of these under a seat, for example.
  • Those controlled by an electronic device (PC, laptop, tablet, or smartphone). Your device connects to the DSP via USB cable or a wireless Bluetooth connection. These DSPs use software that is loaded with extra tools, offers more frequency bands to adjust, and allows for intricate setups.

    The downside is that you have to do everything via the software. That means having your portable device handy and the time to do it. But oh boy, the things you can do!

The power option

Another consideration is that there are a few high-tech power amplifiers that have full-featured DSPs built into their circuitry, eliminating the need for a separate amp and processor. If you're starting from scratch and need both, one of these amps can give you everything you need.

The downside to the combination unit is that if you ever want (or need) to change amps, then you'll need find a new DSP (or another amp that has it built in) and set up your system all over again. With an outboard DSP, you can change amps when you want and then just tweak the DSP to accommodate the new amp's performance.

Equalizer graphic

Equalization (EQ)

An equalizer is like tone controls on steroids — instead of just two controls, treble and bass, there can be as many as thirty, each controlling the volume of a very narrow band of frequencies.

The goal of adjusting the EQ is to end up hearing every note, high to low, equally well. The acoustic space in most vehicles is so unfriendly to a system’s frequency response that applying a lot of equalization is often the only way to make it sound good. 

Time alignment graphic

Time alignment

Your front and rear speakers are all at different distances from your ears, which means that the sound from each speaker will arrive at different times, making the soundstage off-balanced. Depending on where you’re sitting, you’ll hear more or less of certain parts of the music.

Time alignment delays the sound of the speakers closest to the listener’s position and makes sure that the sound of each speaker arrives at the same place at the same time, centering the stereo image for that listener.

Bass enhancement graphic

Bass generation

Everybody likes to turn up the bass in their music — only sometimes the factory stereo automatically turns down the bass signal in order to protect cheap factory speakers.

A solution some DSP manufacturers offer is a bass restoration circuit that generates bass tones one octave lower than the lowest notes detected. This helps restore the bass frequencies that the factory stereo is blocking.

Crossover graphic


Most programmable DSPs offer a wide selection of crossover types for a variety of setups and sounds. These crossovers let each speaker focus on the parts of the sound that it produces best. For example: 

  • You don't want to send low-frequency notes to a tweeter because they'll destroy it — so you roll-off low-frequencies with a high-pass filter.
  • For a subwoofer, the high frequencies are eliminated so the sub can focus on bass.
  • For midrange drivers, like door speakers, you'll want to use "bandpass filter” mode, where a high-cut filter keeps the tweeters' signals away while a low-cut filter removes the sub's frequencies.
JL Audio tuning software

Channel mixing and assignment

Maybe your car’s factory system has separate pre-tuned or amplified signals going to, say, factory subs, mids, and tweeters. You'll want a DSP that can combine them into one smooth, unified signal for you to balance, align, and tune for your better-sounding components. It should also give you the choice to assign any signal or combination of signals to any amp or speaker you want.

AudioControl oscilloscope app

Professional tuning tools

Pro installers use several high-end tools to tune an audio system. There are five important tools that installers use to make systems sound perfect: an RTA (or real-time analyzer), a voltmeter, a polarity checker, an SPL loudness meter, and an oscilloscope to see signals. Most of us don't have access to any of these tools. Luckily, we still have other options.  

Digital sound processor software

DSP software does a great job of letting you fine-tune. You’ll typically get a built-in real-time analyzer (RTA) that visual­izes system response across the entire spectrum. This helps you make precise adjust­ments. And for high-end installers and serious hobbyists, there are more tools and devices out there to help dial in the sound to perfection.

A phone-friendly measurement mic and app
Another way to visualize and measure the acoustic characteristics of a system is to use a calibrated measurement microphone, like AudioControl's SA-4100i, that plugs directly into your compatible device running a measurement app. The SA-4100i's suite of measurement tools includes an RTA, a polarity checker, and a loudness meter.

Not sure? Call us

Those are the terms and features that you need to know when shopping for a digital signal processor. Give some thought to what you need in your system then take a look at our selection of EQs and DSPs

An Advisor can help you pick out a DSP with the tuning features you want that also has the adjustments and controls you'll feel comfortable with and enjoy using. Give us a call.

  • Jason Cooper from Lafayette

    Posted on 12/22/2022

    I have put Hertz components in the doors of my 2018 Fusion with Sony Premium stereo. Should I get a DSP first and get a 5 channel amp later or vice versa?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/26/2022

    Jason, A DSP will process the factory signal for an aftermarket amplifier, so it's best to get them both at the same time - even in the same package, like an amplifier with a DSP built-in.
  • Joseph from Las Vegas

    Posted on 8/3/2021

    If I am going to put a DSP, should I just turn my amp frequency crossover all the way up and set the crossover on my DSP? I have a 4ch and mono, so High pass and subsonic should be turned up then adjust everything on DSP? I'm planning to get the audiocontrol DM-608. Thanks for the response.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/3/2021

    Joseph, A DSP comes before the amps in the signal chain, so after all the tones and crossovers are set in the DSP, you should turn off any high- and low-pass filters on the amps, or set them for the least interaction between all the active crossovers - usually at the highest possible frequency value.
  • James Thompson from Cave City

    Posted on 6/29/2021

    I have a Sound Stream Digital Bass restorer and recently I acquired a sound stream 7500 watt amp with the digital base restorer installed in it . Can I have them both hooked up. Like will it harm either because this amp probably gets half that amount of watts. I have a 6000 farad capacitor hooked up to it . I'm pushing Two 15 inch Q power dvc 2200 watt 600 rms. And how do u figure the best settings? This should be way louder and there is a constant humming noise as soon as I turn the power on to my head unit? Thank you for your time.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/30/2021

    James, Adding restored bass to a signal that already has its bass restored will probably result in distorted, overloaded bass-rumbling noise. For help with the settings, check out tuning your subs.
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