As a DSP engineer, I work extensively with digital filters to modify audio signals. Because we humans have a tenancy towards confirmation bias, I tend to see filters wherever I go. Lots of time it has to do with how we perceive audio. For instance when we hear audio coming from another room, it sounds muffled since low frequencies transmit through solid objects better than high frequencies.
I also find myself figuring out the standing modes of rooms. These are the resonant frequencies that tend to dominate certain spaces. They are especially evident in bathrooms, garages, and empty rooms. It is actually quite easy to do this yourself. Simply start humming at a low pitch, and then increase your pitch until you start to feel the sound increase in volume in your ears. Pretty soon, you will be able to pick out a specific pitch that seems to make the room “sing”. That’s a room mode. And if you go up an octave, you’ll find another mode.
Why does this work? It’s actually a similar principle to why you can make a wine glass generate sounds. The structure that you are “ringing out” has an inherent frequency that corresponds to its size. In the case of the wine glass, the structure will vibrate at a certain pitch when stimulated by fingers running around the rim. In the case of the room, the sound waves will bounce off the walls in response to your humming. Normally the sound waves bouncing off all the walls and the ceiling roughly cancel out each other. But at certain frequencies, the sound wave that bounces between two opposing walls add up and reinforce each other. So a resonant mode occurs, and the result is a huge spike in a room’s frequency response.
I’ve found myself in a couple of awkward situations doing this hum test, in a space I thought was unoccupied. Explaining my actions to someone who isn’t an audio engineer is a completely fruitless endeavor.
But what fascinates me even more is the metaphor of ourselves as a filter. To explain this, we need to know what constitutes a filter.
FIR and IIR Filters
There are two major types of digital filters, and I’ll try to explain these in completely non-DSP terms. Finite Impulse Response (FIR) filters work by storing the incoming audio as it occurs. The filter can take these past values and multiply them by individual numbers ((called coefficients), and then all of these multiplied numbers are added together. Depending on the value of these coefficients, the filter can be made to be a low-pass filter (passing low-frequency sounds and filtering out higher-frequency sounds), high-pass filters (the opposite of low-pass filters), band-pass (passing audio surrounding a certain pitch and filtering the rest), among many other kinds.
An Infinite Impulse Response (IIR) filter is similar, except that the output audio (after all of the values have been added together) are also saved. These output values are saved and will be multiplied by individual coefficients, and then added along with everything else to generate the actual output audio signal. Again, you can have low-pass, high-pass, and band-pass filters among others.
We are all filters
So how does this related to ourselves? Let’s talk about self-awareness. How is an FIR filter aware? It is aware of its input audio, it is aware of the coefficients applied to the inputs, and then generates an output. An IIR filter is aware in the same way, except it is also aware of its output and can even apply coefficients to its current output to further modify its future outputs.
Think of that in terms of people. We have 5 senses. Usually, we use these sensory inputs to take action based on our external surroundings. So when we feel the sun on our skin, smell salt water, and hear the sounds of seagulls, we might breath in deeply and stretch out our arms to increase the amount of the good sensory inputs we’re receiving. In a sense, we’re increasing the coefficient that corresponds to that input. When one sense gets “out of whack” such as when we are in a noisy urban construction area, we have the ability to “decrease” the coefficient of our hearing in order to ignore it.
But like an IIR filter has output coefficients, we humans are also able to tap into the signals we are giving off, and figure out what we need to change so that we generate the output that we desire. For instance, most of us know the feeling where we are talking way too loud for where we are – it causes us to immediately quiet ourselves. It’s the “indoor voices” lesson, and something that people learn in elementary school. Except some people don’t learn that lesson. Or even more importantly, we don’t learn to adjust our output coefficients.
We should all strive to be IIR filters
At its very basic core, this concept of adjusting output coefficients to change the signals we generate is the concept of “self-awareness”. But some people don’t understand that they can change their output coefficients. Maybe they don’t know how, or they just don’t care. But for some reason they still expect others to adjust their coefficients.
Shouldn’t one of our fundamental life goals be to figure out how to best interact with others? Isn’t the very core of that learning to interact well with people? Of course, it is equally important to adjust your input coefficients so that you don’t get overwhelmed with life.
I’m sure you could take this metaphor further, to philosophize what it means for someone to be a low-pass filter or a high-pass filter. But I’ll leave that as the proverbial exercise to the reader.