Your Hearing is Amazing!

If we could not hear, there would be no music, and no music recording. This episode explores the characteristics of our hearing, it's limitations and idiosyncrasies, and how to preserve your hearing. We look at the range of frequencies we can hear, and look at the quietest thing we can hear -- and the loudest noise we can tolerate. We can damage our hearing while we are doing surprisingly mundane tasks. If you prevent this damage, you can appreciate the full impact of music your entire life. I cover how to protect yourself from hearing damage. Includes sample sounds.

email: dwfearn@dwfearn.com
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Transcript

Speaker 1: 0:00

I'm Doug Fern and this is my take on music recording. This is a show about the intersection between music and technology. Without technology, we wouldn't have recorded music, and I wanna explore how the technology changed the music and how the music changed the technology. This series is intended for those that are curious about how the recording process works. That could be the audio file or someone who just enjoys listening to their favorite artist . It's not gonna be very technical, but more a philosophy of how recording is done and why recording engineers do what they do in order to provide the best listener experience. So in this first show, I'm gonna talk a little bit about your hearing, how it works, its limitations, its idiosyncrasies, and illustrate some of these points with some tones and and other audio samples. Obviously we wouldn't have music and we wouldn't have music recording if we were incapable of hearing sounds that came to us through the air. Let's first take a look at the range that you're hearing covers. The range of frequencies or the range of notes that you can hear is generally accepted to be from about 20 hertz at the low end to about 20 kilohertz on the high end . Both of those extremes are really out of the range of most musical instruments, but we need that full range in order to fully appreciate the sound. So what do these frequencies sound like? I'm gonna play a few tones for you in order for you to get a sense of how this works. You would think from your hearing range of 20 to 20,000 hertz, that the middle would be about 10,000 hertz, but our hearing doesn't work that way. We hear things in terms of octaves. An octave is just a sound that's exactly twice the frequency of another sound. For an example, here's a 440 hertz sound. This is a pure sine wave . Tone instruments don't make pure sine waves like this, but they're handy for us to illustrate the principles. Here's 440 hertz and now we're going to hear a sound that's exactly one octave above that, or 880 hertz. To give us a sense of where the middle of our hearing range is, I've chosen to play a 640 hertz tone. This is pretty close to being exactly in the middle of your hearing range. In other words, you can hear the same number of octaves below this as you can octaves above this. Obviously this is a long way from that arithmetic average of 10,000 or so. Now I'm gonna play 20 hertz and 20,000 hertz so you can hear what the extremes are. I doubt that very many of you will actually hear these tones because most home systems will not reproduce these extremes very well and your hearing is actually quite insensitive at the very low and very high frequencies. Here's 20 hertz And here's 20 kilohertz. Now if you have some sort of meter on the system you're listening to, you may actually see the tones appear, but you probably didn't hear them. Most people beyond their teenage years really can't hear that top octave from 10,000 to 20,000 hertz anymore, and that's a result of continuing abuse to your hearing, which can occur in a lot of ways that you wouldn't expect, and we're gonna talk about that later on. So since those frequencies aren't particularly well reproduced or heard, let's try something. Let's go up one octave from the bottom and down, one octave from the top. So the next tone you're going to hear is 40 hertz. It's an octave above the 20 hertz tone we had before, And here's 10,000 hertz. This is an Octa below the 20,000 hertz we played before. Now I'm gonna bet that most of you heard that 10,000 hertz tone , the 40 hertz tone depends on your system. You probably have a better chance of hearing that if you're listening on a really high-Fi speaker system or with quality headphones, you're a lot less likely to hear that if you're listening on computer speakers, laptop speakers, and maybe even with earbuds. That gives us a sort of benchmark so we have a sense of when we're talking about these frequencies, what they actually mean. So in terms of octaves, we can hear 10 octaves from 20 hertz to 20,000 hertz, but what about the loudness range our hearing can accommodate? The scientific definition of the quietest sound we can hear is called zero db SPL. Well , that's a lot of gobbledygook. What does that mean? Well, for one thing, the DB or decibel is a handy tool used in audio and actually in a lot of scientific endeavors in order to characterize the relative level between two sounds. So the decibel really started out as a unit called the bell named after Alexander Graham Bell, who invented the telephone. That was a pretty crude unit. So the decibel are one 10th of a bell as become the most useful for us. Decibels are logarithmic measurements. So if a sound increases by 10 db, it's actually 10 times the level, but if a sound increases by 20 db, it's actually a thousand times louder. Just like the octaves in our frequency range, the logarithmic unit of the decibel is better suited to how our hearing actually works. Since a decibel is just a ratio between two levels, it has to have a reference point or else it's pretty meaningless for hearing. We use a reference level called SPL, which stands for sound pressure level, and there's a really scientific explanation of what zero DB SPL is, and we won't go into that, but just accept that as the quietest sound you can hear. Now the quietest sound I can hear and the quietest sound you can hear and the quietest sound a 5-year-old can hear and the quietest sound an 80-year-old can hear are all gonna be very different. So we have to take these numbers with a little bit of a grain of salt, but it does give us a sense of exactly what the range our hearing can accommodate. If zero D-B-S-P-L is the quietest sound we can hear, what's the loudest we can hear? Well, this is kind of an arbitrary upper limit that's defined, but it's usually accepted That is at the point where your hearing experiences pain and that level can be anywhere from 120 to 130 decibels, SPL. Those levels are really loud and they will cause almost immediate damage to your hearing. Let's look at some levels of common sounds you might encounter in your daily life and see how they compare. Once again, we can't take these as absolute because everybody's hearing is different and it's greatly dependent on the measuring technique. As a general rule, most sounds defined in SPL are at one meter or about three feet away from the source of the sound, but that's not really practical in every case. So we sort of have to make a mental adjustment to accommodate for the different distances where we're measuring the sound. So let's start with something really quiet like a ticking of a watch. If you put a watch up to your ear, what you're hearing is about 20 DB SPLA whispering voice is about 30 db. If you go outside in a quiet neighborhood, you're probably experiencing about 40 db. The refrigerator running in your kitchen is about 50 db. The background level of most households is about 50 to 65 db, and conversation is also about 60 db. When you get in the shower in the morning, you're exposed to about 70 db. Your typical restaurant is about 85 db. Your blender generates about 90 db, a symphony orchestra and a concert hall at its loudest peak is about 110 db. A rock concert is about 120 db, which is about the limit of the threshold of pain For many people, 120 DB is also the level of most sirens. A chainsaw is about 125 db. If you go to a sports stadium with an enthusiastic crowd, their cheering might reach 130 DB and firing a gun exposes you anywhere from 150 to 170 db. For people that work with those that are disabled by losing their sight or losing their hearing, generally report the people that lose their sight do much better than the people that lose their hearing. I may not be entirely objective, but I believe that your hearing is your most important sense . Let's compare the dynamic range of vision and hearing between the quietest sound you can hear and the loudest sound that you can tolerate is somewhere between 120 and 130 db. That's a range of over 1 trillion to one. If our hearing has a dynamic range of 120 db, our vision only has a dynamic range of about 90 db, so our hearing dynamic range is about 1 trillion, but our vision dynamic range is only about a billion. Still pretty amazing, but your hearing is obviously better at this. And how about the frequency response? The accepted typical range of our hearing is 20 hertz to 20,000 hertz attend octave range as we've talked about, but our vision responds to electromagnetic waves, which are much, much higher in frequency in a different mechanism than sound, but our vision only covers less than one octave to accommodate a wide range of light levels. Our pupils in our eyes automatically adjust in order to bring in more light when it's dim and block out more light when it's bright out. This works pretty well and allows us to have that 1 billion to one range in our vision. And as you've experienced, if you come in from a bright sunny day into a dimly lit room, it takes a little while for your eyes to readjust to the lower light level. In fact, it can take up to 20 minutes going from brightness to darkness until our full sensitivity is restored. So obviously it isn't just the pupil, but there's also chemical reactions going on in the retina in your eye that take time to recover. You might think our hearing does not have a comparable mechanism After all, the physical size of the opening of our ears does not change with the level of the sound we're experiencing, but there is a mechanism inside your inner ear, which we cannot see that actually changes when exposed to loud sounds. It automatically reduces the volume by a significant amount very, very rapidly and then opens back up again in order for us to hear quieter sounds. I read about that many years ago and I thought it was very interesting, but I had a real practical demonstration of that when we were building my first recording studio. There's a lot of construction going on with hammering and sawing, and I realized that when listening to the sound of a circular saw while somebody near me was hammering a nail, that the sound of the circular saw decreased each time the nail was hit. It quickly recovered after each nail hit, but it wasn't instantaneous, but certainly a lot faster than 20 minutes it takes for your vision to recover. This mechanism is designed to protect our hearing from loud sounds, but our hearing mechanism does not respond fast enough to a very abrupt sound and that can cause damage. A gunshot would be an extreme example of that. Only in the most sophisticated audio systems is it possible to reproduce the full 120 DB range of our hearing. So obviously I can't give you an example of that, but I can give you an example of what 20 DB sounds like because you'll still be able to hear my voice if it's decreased by 20 db. Nothing else has changed except the level of my voice has now been reduced by 20 db, so it's now one 1000th as loud as it was before, and now we're back to the normal level. In our audio equipment, we're always looking for perfect frequency response from the lowest frequency to the highest, from 20 to 20,000. In the audio world, this has turned flat response because if you were to graph it, it would be a straight flat line. We're very good at detecting even minute changes in that flatness of the response. For example, here's my voice with a frequency response cut off below 300 hertz. We can do the same thing with the high frequency response. Let's cut it off at 3000 hertz . Here's my voice with everything above 3000 hertz eliminated, and here's an example of everything below 300 cutoff and above 3000 cutoff. It's interesting, we can eliminate those low and high frequencies and just leave a range, which is less than four octaves and still understand speech pretty well. In fact, that 300 to 3000 range was pioneered by the telephone company over a century ago in order to determine exactly what was needed to not only understand speech but also recognize the voice of the speaker over a telephone. Our hearing is most sensitive to the frequencies around the speech range and the differences are pretty extreme. In fact, in order for a sound at 20 hertz to sound as loud as it does at 3000 hertz, the sound has to be about 70 DB louder. That's an extremely big difference. At the high end , a 20 kilohertz signal needs to be about 10 DB louder than it does at 3000. In order for us to perceive it as equally loud and to further complicate this, the drop off in sensitivity at the low end and the high end varies with the absolute level of the sound. So the louder the sound, the easier it is for us to hear that very low 20 hertz or that very high 20 kilohertz. This characteristic of our hearing was defined very accurately by two bell lab scientists in the 1930s, Fletcher and Munson. The curves that result from that are called the Fletcher Munson curves, and although further research has refined them somewhat, they still pretty much had it figured out. Bell Labs was amazing in their ability to define almost everything we know about audio, including digital audio in the 1920s and 1930s. Since the frequency response of our hearing varies so much with the loudness that we're listening to, it's important that the recording engineer listen to the balance between the instruments at roughly the same level that you're likely to be listening to it at home. It's almost impossible to accommodate every potential listening situation while recording. So we have to make some assumptions about how loud people are gonna be listening to something. Here's another odd idiosyncrasy of our hearing, one that's pretty subtle, but once you become aware of it, you'll probably notice it, and that is our perceived perception of the pitch or frequency of a sound varies with the volume. For example, if you're listening to a song at fairly loud volume and the song fades out at the end, you'll notice that as it fades out, it will tend to go flat. Or in other words, it'll sound like it's going out of tune to the low end of the range. If you have some musical training, this will probably be much more obvious. Whether you're a recording engineer, an audio file, a dedicated listener, or a musician, your hearing defines who you are. And so it's very important to take good care of it. We know that in our society age has a big effect on our ability to hear sounds both in level and in frequency response. I find it interesting that people that live in naturally very quiet environments where they're only exposed to the sounds of nature and human voice maintain their excellent hearing into old age. In our society, it's not unusual to have somebody in their teenage years already with a hearing deficit. This can be explained by the noisy environment in which we live. If we think back to those sounds that we encounter every day in our lives and look at the actual level of them in D-B-S-P-L, we can see that we're exposed to a lot of really loud sounds in our lifetime. Loud sounds might not be instantaneously damaging to your hearing, but a lifetime of exposure to those sounds will cause damage. These problems with our hearing generally first manifest themselves as a loss of high frequencies. In fact, I'd be willing to bet the majority of you out there listening cannot hear anything above 10 kilohertz. That's only the top octave of our 10 octave range, but it is significant and it does change the way we hear things. It used to be in the days of the cathode rate tube TV sets and computer monitors that we could often hear the sound generated internally of these devices, which was about 15,750 hertz or pretty close to the upper range of our hearing frequency response. This was caused by circuitry in the television set that used that to provide the horizontal sweep for the painting. The picture on the cathode rate to this no longer exists with typical flat panel displays, although they can generate their own high frequency noises. So those of us above a certain age can remember when we would walk into a room with a TV set operating and immediately hear that 15,750 hertz signal. Some of us found it very annoying, particularly if you were close to the TV set. By the time I was in my thirties, I could no longer hear that unless I was really close to the tv. So I knew I was losing some of the high frequency response. And as I record this, now I'm 71 years old and I can hear 10,000 hertz pretty well, but my hearing above that drops off pretty rapidly, and that's typical and you don't have to be that age in order to have that problem. In fact, testing has showed that many 18 year olds have hearing that's worse than mine. So why is my hearing still pretty good after all these years? I think it's because I've always been annoyed by loud noises. I grew up in a very quiet area and a quiet household, so I wasn't exposed to that much loud noise to begin with. If somebody was using the vacuum cleaner and came into the room where I was, I had to leave. It was just so loud and annoying to me, I had to get out of there. Even to this day when I use a vacuum cleaner, I put on hearing protectors not only because I wanna preserve my hearing, but I find that sound just extremely annoying. So my oversensitivity to loud noises has actually served me pretty well and preserving my hearing. How do we measure and determine how our hearing is doing? Well, it really takes some pretty sophisticated equipment in order to do it with great accuracy, and that's what an audiologist does. The field of audiology is mainly concerned with your ability to hear and understand speech. Actually, their standards are completely silent on your ability to appreciate music. What can be considered the threshold of abnormal hearing is pretty extreme. They normally test with pure tones that range from 250 hertz to 4,000 hertz. That range covers the range of speech pretty effectively. And if you can hear in that range, you should be able to hear speech pretty well. You can have up to 25 db of loss in the sensitivity of your hearing, and it could still be considered normal. Here's an example. This segment is recorded 25 DB lower than the rest of the audio. So our hearing is tested on a four octave subset of our 10 octave range, and that's the range's important to us functioning in life. But we do need more than that if we wanna fully appreciate music. So if you care about your hearing, it's important to take precautions to protect it and some everyday activities. As we've seen produce sounds that are pretty loud standards throughout the world on how loud workers can be exposed in the workplace for an eight hour shift, generally define it as about 85 DB SPL . That's about as loud as it is in a typical restaurant, and it's a little quieter than a blender in your kitchen. That 85 DB SPL limit was designed to protect workers from losing their ability to hear speech. It does not mean that their hearing won't be impaired by exposure to levels lower than 85 db. Some things you do every day are probably damaging your hearing. One shocking example is driving. If you are in a car with a window open above 35 miles an hour, the sound level is high enough to cause damage to your hearing over time. I didn't know that statistic when I first started driving, but I did know that I hated the sound with the windows open and even before the days of air conditioning, I would suffer in sweat rather than to be exposed to that high level. I close the windows all the time. Other everyday sources of sounds that damage our hearing are most tools, even hand tools like a hammer. Anytime you're using any kind of power tool or even a hammer, it probably makes sense to use hearing protection. Certainly it makes sense to protect your hearing if you're gonna be using a lawnmower, a leaf blower, a snowblower, or a chainsaw, all those things will cause damage. Our hearing provides us with clues to let us know that we're damaging our hearing. If your ears are ringing after a loud sound or coming out of a concert, you know, if you've been exposed to sounds that are high enough, that's probably caused some degree of permanent damage. But there's another phenomenon you might experience with sounds that don't cause instantaneous damage but will over time, and that's what's called a temporary threshold shift. You've probably noticed this. If you've come out of a concert or the movies and your hearing seems to be somewhat subdued, maybe your car seems exceptionally quiet on the drive home. The assault on your hearing has caused it to semi permanently stop down the level. It will recover on its own in most cases. But this temporary threshold shift could last for minutes to hours. I became aware of this early in my recording career and I realized that it wasn't doing me any good If I had a temporary threshold shift, I knew I was listening too loud. And the frequency content of the sounds also has a big effect on creating a temporary threshold shift. Those frequencies in that high sensitivity range of your hearing around three kilohertz will create a temporary threshold shift much more rapidly than a sound with a lower frequency content. I became aware of this a few years ago when our power went out during the summer and it was too hot to stay in the house. So we slept out on a screened in porch. We live out in the country and we're surrounded by insects that make a huge amount of noise at night. I realized after a few minutes of being out there that not only was I not gonna be able to sleep with this racket going on, but that it created a temporary threshold shift. So I came back inside, got my earplugs and went back out. So I think it's a good idea to pay attention to this, and if you experience a temporary threshold shift or worse ringing in your ears, make sure you avoid those kinds of things because it's gonna affect your hearing. Maybe not today, but eventually we know that constant exposure, eight hours a day to 85 DB SPL will eventually damage your hearing. But does damage occur at even lower levels? It probably does because our hearing evolved in a very quiet environment. Our society today is much noisier than it was when humans first emerged. So how loud is too loud? Well, we know if you have the temporary threshold shift or the ringing in your ears, that's much too loud. But how loud does it have to be to cause damage? And that's a really good question. I check to see and recording sessions just how loud I had the monitored speakers turned up at my listening position and I found that the comfortable level for me was about 65 db, which is pretty quiet by most people's standards. That's in the range of conversational voice. But I found that listening at up to 75 DB not only was potentially damaging to my hearing, but it was becoming very annoying that loud. So think about that when you're listening to your music because it's very easy to get carried away and turn up the volume if you're enjoying the music. If you're listening with headphones or earbuds, it's even more dangerous because they can produce a huge amount of sound that'll damage your hearing easily. Often during my recording career, there were times when the performers and the producer wanted to hear the playback much louder than I was listening to it during this recording. I wasn't about to subject myself to that, and I had a control room with speakers in it that were easily capable of 120 DB threshold of pain levels. So what I would do is back up the recording about 10 seconds before the music began, turn up the volume, and then slip out the door and close the door behind me. The performers enjoyed the high level and I avoided hearing damage. Almost all the musicians I know have some degree of hearing impairment. Some of them , it's pretty serious. A lifetime of performing on stage really takes its tolls on performers, and you'll see many of the rock stars from the sixties and seventies now having a difficult time hearing wisely. Many of those have gone to in-ear monitors so they're not exposed to the extreme levels on stage. The levels into their ears can be more carefully controlled, but even musicians that don't play very loud instruments can suffer hearing damage. Almost all violinists suffer some damage to their hearing in their left ear over time because their left ear is very close to the source of sound from the violin, it's exposed to very high levels. Remarkably, most musicians, despite significant hearing loss, can still perform very, very well. Many musicians continue performing up into their seventies and still do perfectly well, even though their hearing has been significantly compromised. If you wanna preserve your hearing here , the full range of frequencies, hear the quietest passages in the music. It's important to protect your hearing. Please don't wait until you need hearing aids in order to function in the world. This is my take on music recording. I'm Doug Fern. See you next time.