HPF and LPF Settings on Head Unit

What Are HPF and LPF?

HPF: The following abbreviation stands for high-pass filters that we use in head units to restrict the range of frequencies that are sent to the coaxial speakers or subs. They block low-frequency response (restricting bass frequencies) from playing, resulting in a cleaner sound as a result. High-pass filters allow higher frequencies, resulting in better clarity and accuracy for mid and high-range notes. It also helps you to reduce any unwanted vibrations or buzzing sound caused by low-frequency audio signals from the sound system.

LPF: The following term stands for low-pass filter on a receiver and is typically used to block high frequencies and allow bass frequencies to come through. This crossover filter will allow you to enhance low-range sounds like bass drums, and you can easily hear the synthesizers more clearly. The frequency cutoff point for a low pass filter that you can usually adjust manually so you can customize the audio output according to your preference. Generally speaking, lower crossover points will produce heavier bass notes, while higher crossover points will bring out more treble frequencies.

Why Do You Prefer Adjusting the HPF and LPF Settings on Head Unit?

As mentioned above, adjusting these filters can help you get the most out of your system, ensuring you achieve the best sound quality possible. Using an HPF or LPF can help reduce noise in the audio signal. By using a high-pass filter to cut low frequencies, you can minimize background noise and hums that may be present in the signal.

On the other hand, you can use low-pass filters to reduce high frequencies. This is beneficial for removing sibilance from vocals and creating a smoother overall sound. By removing these higher frequencies, the mix will have less harshness, resulting in a more balanced sound.

How to Set High-Pass and Low-Pass Frequency Filters on a Car?

It’s not rocket science. You can get the best output from your car subwoofers or even component speakers ⁽¹⁾ by adjusting the HPF & LPF through these simple steps:

1. Identify the Filter Types for Your Car Audio System:

It is essential to know the type of filter present in your car’s audio system before attempting to adjust it. If the system has a built-in filter, you can usually identify it by looking at the stereo’s user manual or checking with the manufacturer. Alternatively, you can use an oscilloscope to check for frequency crossover points between the speakers and the subwoofer.

If your audio car system does not have a built-in filter, then you may need an external signal processor like an equalizer (EQ) or active crossover unit ⁽²⁾ with a high-pass (HPF) and low-pass filters (LPF). These filters will allow you to adjust frequencies independently and ensure each speaker receives its share of power from your vehicle audio amplifier.

2. Know the Frequency Range of Your Subwoofer:

Knowing the frequency range of your subwoofer is essential before setting up a low (LPF) and high-pass filter (HPF). The LPF will determine your desired highest frequency response, while the HPF will block any audio signals below a specific frequency. You can find the appropriate cutoff frequency for these filters in the user manual or online. Knowing this information will help ensure you get plenty of power out of your system without causing any distortion.

3. Set the High Pass Filter:

You can set the high pass filter on your receiver by following the below points:

Check if Your Head Unit Has High Pass Filter: You must ensure that it contains the HPF option by looking in the user manual or the receiver’s menu options. Not all car audio stereo receivers have this feature, so double-check before deciding on a particular model.

Set the HPF: You can quickly set the high pass filter by determining the range of your car subwoofers or coaxial speakers and setting it slightly below than it. I mostly start with a good frequency range of 80Hz and then adjust it according to my speaker’s specifications.

Navigate to Eq or Crossover Settings: Now, you must navigate to the equalizer or crossover menu to adjust the high pass filter option on the car amp. You can then make changes based on your preferences.

Adjust the HPF Settings: Depending on the model, these may include setting the slope that determines how steeply the filter cuts off frequencies, choosing a cutoff frequency at which it begins to roll off, and adjusting its level. Experiment with different settings until you achieve the desired sound for your vehicle’s front or rear speakers. As mentioned above, you can start with 80Hz, a good frequency for most audiophiles.

4. Set the Low Pass Filter:

You can set the LPF on your car stereo receiver by following the below steps:

Determine if Your Head Unit Has Low Pass Filter: As you did for the HPF, check the user manual or audio system menu options to determine if your system has low pass frequency filters. Some vehicle audio systems already have a built-in feature, while some may require an external signal processor.

Set the Low Pass Filter: To set, determine the frequency range of your rear speakers. Then adjust the low-pass filter slightly above the highest frequency response; typically, around 70 to 80Hz is a good starting point. (The given Hz works like a charm in my car audio system)

Navigate to Eq or Crossover Settings: Now, navigate to crossover or equalizer settings to adjust the LPF. You can make the changes on your head unit according to your preferences or the Hz level (Also measured in KHz) I’ve shared above.

Adjust the LPF Settings: You can adjust it by three control parameters: the slope, which determines how quickly frequencies you can reduce; the cutoff frequency points, which determines the frequency at which filtering begins; and the level of filtering, which determines how much noise is blocked from entering into your speakers.

5. Test the Settings:

To test a low-pass filter, start playing music and adjust the settings accordingly. Listen for any distortion in the sound, indicating the slope or cutoff frequency that you need to change. The level of filtering may also need to be adjusted depending on how much noise is coming through. To test a high-pass filter, listen for too high or distorted frequencies. If required, you should change the slope and cutoff frequency so that your component speakers aren’t getting overdriven by specific frequencies.