This article is about using high pass filters for the bass guitar. To learn about differences of active and passive bass guitars, see our article here. You can also view our courses.
A High Pass Filter (HPF) can be a great solution to sonic problems that are hard to define and secretly lurk in the world of bass guitar. Understanding what a HPS does, and its benefits, will lead you to solving some of these elusive and hard to define sound issues.
What does a high pass filter for bass guitar do? A high pass filter removes low frequencies while allowing higher frequencies to pass through. A more focused tone, increased speaker efficiency, and speaker protection results from the use of a HPF while playing bass.
Let’s take a look at seven important things a high pass filter will do for the bass.
How An HPF Works
A HPS allows higher frequencies to pass through the signal chain, while lower frequencies are blocked. It works similar to a gatekeeper; if you have the correct password, you are allowed to enter, but if not, you must remain outside. Furthermore, an HPF uses a sloped cutoff. This would be analogous to a common area where a certain number of people, without a passcode, are allowed to gather around the gate, and a few of them slip in with the valid passcode holders. Practically speaking, this means that if the HPF is set for a cutoff at 30hz, in actuality, some lower frequencies will come through because of the slope. Therefore, to absolutely cut off any frequencies below 30hz, a higher setting is necessary, e.g. 35hz.
An HPF will help to focus the sound of your bass by cutting out lower frequencies that produce a muddy or unfocused sound. (The overtones of these fundamental tones are also unfocused, and because the overtones are in a more audible range; the focus of the overall tone is diminished.) Let’s take some examples: The lowest frequency of a four string bass is around 41hz, this is the low E string; the lowest frequency of a five string bass, the B note, is around 30hz. By setting an HPF to 40hz and 30hz, respectively, you will be eliminating all of the unwanted frequencies that muddy the tone. Of course, your ear should be your final guide for exact settings; but, this will give you a starting point.
This is one of those things that you usually don’t figure out until it is too late; that is, you have a blown or damaged speaker. Keep in mind, a HPF, is much cheaper than a new speaker cabinet. So, some prevention is definitely a good thing here. Now, many bass amps have a built in HPF just for this reason; but, if you are not sure if your amp, especially a vintage amp, has this added layer of protection, an HPF is an essential piece of insurance for your amplifier. Most speakers are tuned, that is designed, to efficiently produce frequencies as low as 40hz.
This makes sense, because that is the frequency of the low E on a four-string bass. The speaker will produce frequencies lower than designed, but at a cost to the structural integrity of the speaker and sound quality. Sustained frequencies, below the designed threshold, will push the speaker to move in a free and uncontrolled manner, which can lead to speaker damage or failure. A HPF will help to control speaker movement in a manner consistent with its design, especially when frequencies below its optimal threshold are crossed, e.g. a five-string bass with a 30hz low B string.
When the amplifier is not powering and driving unnecessary low frequencies, it can operate more efficiently. There will be more power for the actual frequencies that are for the music; and therefore, the amp will have more headroom, which will enable it to play louder. In some cases, you will see a twenty-five to fifty percent increase in volume when using a HPF. Again, this is something that you do not know that you are missing until the low frequencies are eliminated and you experience the results.
Because an HPF eliminates the lower frequencies that tend to muddy and cloud up the sound coming out of the speaker, by sending a more focused signal to your effects pedals, your processed sound has the potential to be less cluttered by unnecessary frequencies. Of course, this is subjective, and you may find that you like this sound; however, having the ability to manage which frequencies are sent to your effects units will give you more control over the final sound that you are hearing.
Prevent Ear Fatigue
This is another one of those things that you won’t be able to appreciate until you experience it. Remember, because bass speakers are “tuned” for frequencies in the forty to fifty hertz range, the overtones of the frequencies lower than this range will be unfocused, but, never-the-less, amplified along with the “tuned” overtones.
The unfocused overtones will cause the ears to fatigue over time, which creates the all too familiar phenomenon at the end of a loud gig, of not being able to distinguish tones very well. By eliminating these tones at the outset, your ear will not fatigue as quickly; that is not only healthier playing, it is also more enjoyable.
Bad Room Rising
So, most likely, everyone has had the experience of playing in rooms with bad acoustics. This can be a bass players nightmare. An HPF can tame a bad room very quickly by eliminating the low frequencies that build up in rooms where there is not enough acoustic space to let the sound waves dissipate properly.
The length of bass sound waves are pretty large. This is why the bass sounds louder the farther you are from the speaker. This is desirable for live performance, when everyone involved, by mutual consent, wants to hear the bass. However, when you are practicing at home or in an apartment, not everyone in the house or building, is in the mood for a concert. An HPF can help you to retain your domicile by cutting the low frequencies that will travel through the house or the apartment complex. It is good to play bass, but, generally better, to have a roof over your head!
This is not an exhaustive list, but it is a good place to start. Check out the following: Broughton Audio, HPF-Pre by FDeck, Vong Filterung, and Thumpinator.
Bonus: What is An LPF?
A Low Pass Filter (LPF) works in the opposite direction of an HPL. It will prevent all high frequencies, from a set frequency upwards, from entering the signal path. This can be useful for getting rid of hiss and other high frequency artifacts that you do not want in your sound. An LPF is not as important and useful as an HPF, but it is something to consider. Also, reducing the treble on the bass preamp can eliminate this type of noise artifact as well.
A HPF is a tool that is hard to appreciate until you have used it. It will tighten and focus your tone, prevent damage to your speakers, preserve your hearing, tame the acoustics in a bad room, allow you to play at home without disturbing others in the house, and increase the volume of your amplifier. All of these things make for a more enjoyable and satisfying bass playing experience.