Both can improve car audio, but which is right for you?
Sits between the head unit and the amp.
Allows users to boost or reduce specific sound frequencies.

Lifewire
Generally cheaper than DSPs.
Can send specific frequencies to certain speakers.
Can fix preprocessing issues by fine-tuning the head unit to better match the interior of a vehicle.
Usually pricier than equalizers.
Equalizers Pros and Cons
Cheaper than most DSPs.
Frequency-specific control of audio.
Cannot adjust output for individual speakersaffects the whole sound system.
Adjust frequency performance for individual speakers.
Pricier than most equalizers.
Digital signal processors do the same job as equalizers, but many of them also perform crossover-like functions.
Most factory stereos are designed to compensate forlow-quality speakers, which is accomplished by artificially manipulating the frequency profile.
If you also install an amp, the problem will only get worse.
Thats where a digital signal processor can come to the rescue.
What’s Involved in the Installation of an Equalizer or Sound Processor?
Similarly, most sound processors are designed to be tucked away in the same location as your amplifier.
Some sound processor kits will even plug seamlessly into your head unit and existing harness.