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  1. #1

    Doubt regarding the recording

    Hello Helpers,

    I have a doubt regarding how the microphone is able to record different frequencies at the same time?

    Kindly help me in clearing this doubt.

    Thanks,

  2. #2
    Senior Member SC358's Avatar
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    Hello arun -
    Is there something specifically you're not sure of or don't understand? If not, your question is about one microphone being able to pick-up multiple frequencies? There is something called white noise and pink noise which mics are able to get. To simplify, any musical instruments that can play major and minor chords.


    Whatever you can hear (and sometimes cannot) is what the microphone is trying to convert to electronic form.

    Are you hearing something differently when playing back than what you actually hear?
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  3. #3
    How does a microphone convert different frequencies into electrical impulses (record) at the same time?
    It doesn't.

    How do you hear different frequencies at the same time?
    You don't.

    You hear the same thing the microphone 'records', that is the 'interference' created by the differing oscillations of air compression, creating the movement of "sound." The microphone converts this sound, through varying capacitance, to an electrical signal, you just "hear" through your ear-drum moving in a similar way.
    Eric Adler (tonsofpcs)
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  4. #4
    When you eat cake, you're eating flour, eggs, sugar, lard and whatever else. All part of the whole.

    When you listen to a voice or instrument, you're hearing a combination of frequencies. (Except for a sine wave, which has only a single, pure frequency component.) Normally, you don't perceive them separately, though a trained ear can pick out harmonics - just as a trained cook can taste a cake and tell you its main ingredients.

  5. #5
    Senior Member SC358's Avatar
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    Quote
    Quote: tonsofpcs
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    How does a microphone convert different frequencies into electrical impulses (record) at the same time?
    It doesn't.
    I thought that's what it was doing - if not then what?

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    Quote: tonsofpcs
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    How do you hear different frequencies at the same time? You don't.
    Hmmmm... this is very interesting. So if I were a good musician (which I'm not) musical chords are distinguished because of their harmonics but not individual frequencies? And pink or white noise is just evaluated by our ears as harmonic distortion?
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  6. #6
    Vell, mein schtudents, dis is complicated. How deep do we want to get?

    I'm not sure what tonsofpcs was getting at, but I will try to clarify and maybe I'll just make things muddier.

    When I was talking about a homogenized whole, I was talking about single notes. When you hear a trumpet play A440, the fundamental tone is at 440 Hz. There's also a little 880, 1320, 1760, 2200 and so on. These are the upper harmonics. (I say "upper" because, strictly speaking, the fundamental 440Hz pitch is also a harmonic.) In fact, with a trumpet, many of the harmonics are stronger than the fundamental pitch.

    The ear does not normally hear these as separate tones. What we perceive is the fundamental pitch. Now, anybody who has done audio work has heard a sine wave, which has a sound so dull it's annoying. The reason it's dull is that it has no harmonics. Other kinds of sounds - trumpet, for example - get their characteristic tone quality from the upper harmonics. It is the relative strength of particular harmonics that differentiates a trumpet from, say, a clarinet.

    A chord is a different matter. With a single tone, the harmonic frequencies are mathematical multiples of the fundamental - see example above. With a chord, you have several fundamental pitches which are not multiples of each other. Normally, each of these fundamental tones comes with its own set of upper harmonics.

    Now, back to the original question. Think of a lake that has several stones thrown into it. Each stone will create its own pattern of ripples, which interact and mix with all the other patterns - and yet the lake has only one surface. At any point on this surface, the instantaneous water level is going to be the sum of the influences of all those ripples.

    Likewise, air pressure at your ear (or microphone) can have only one value at a given instant, which is the sum of all the disturbances created by all the sound sources in a room. Mathematically, it's an equation where lots of terms add up to a single number.

    This jumble gets sorted out when it gets past your ears into your brain. If you have, say, a trumpet playing middle C, a clarinet playing middle E, and a violin playing middle G, anyone can hear the three notes and anyone who's paying attention can sort out the three different instruments. That's because the ear and brain are very good at figuring out which harmonics go with which fundamental. Nobody knows exactly how the brain does that.

    Re white noise: a tone is, by definition, periodic - it has a repeating pattern, cycle by cycle - while noise, by definition, does not have a pattern, which is why it has no pitch. I guess I wouldn't call it distortion. Some beautiful sounds, like flutes, have a lot of noise in them and it's part of what makes them beautiful.

  7. #7
    Senior Member SC358's Avatar
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    Quote: karl eilers
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    This jumble gets sorted out when it gets past your ears into your brain. If you have, say, a trumpet playing middle C, a clarinet playing middle E, and a violin playing middle G, anyone can hear the three notes and anyone who's paying attention can sort out the three different instruments. That's because the ear and brain are very good at figuring out which harmonics go with which fundamental. Nobody knows exactly how the brain does that.
    So if you put it in this fashion, we can hear different frequencies from 3 different sources AND be able to distinguish the 3 different characteristics of those sounds - trumpet, clarinet and violin.

    And in answer to arun's question - the microphone can pick-up those different frequencies simultaneously - what do you think Eric? Or is it the mics can't but we (and maybe some cats and dogs) do?

    Btw Karl - your explanations are really great and I'm still learning no matter what I do in life.
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  8. #8
    I never realized how much I like to run off at the mouth until I got on this forum... though I'm sure all my friends have known it for a long time.

    Strictly speaking, neither mikes nor eardrums pick up frequencies. They pick up air pressure variations. It's the brain's job to analyze those vibrations and pick up cues.

    Such as: "Buried deep in this jumble of vibrations, I (the brain) detect a pattern that repeats every 2.27 milliseconds. That means there's a 440Hz tone. There are also tones at 1320, 2200, 3080 and so on. Those are multiples of 440, so I'm going to decide that they belong with the 440Hz tone. They are also all odd multiples. Odd multiples correspond to a 'hollow' sound. The tone is continuous. Therefore, a clarinet is playing A above middle C."

    Of course, the brain doesn't go thru all this scientific reasoning - human brains could analyze sounds a million years before science could. The brain is simply "built" to do this. It has a program put there by evolution or God, take your pick, and it just works.

    This process begins in the inner ear, the cochlea, which is really part of the brain. (There's a reason four of the five senses are located in the head.) If you've ever used or seen a spectrum analyzer, you know that it "sniffs out" and displays the energy present at every frequency within a certain bandwidth - roughly 16Hz to 16kHz for audio - so you can see how much energy is present at, say, 1kHz, 1.5kHz, 2kHz and so on. The cochlea is a spectrum analyzer. There are nerves corresponding to every frequency, with a resolution of about 1/2 percent (roughly 1/10th of a musical half-step), and these nerves send information to the main part of the brain over a massive one-for-one parallel data bus.

    There, aren't you sorry you asked?

  9. #9
    By the way, if you're a guy, you can train your ear to hear harmonics via a singing exercise. (Gals can too, but they'll have to get a guy to sing - you need a low pitch.)

    Sing a continuous, fairly low note. Slowly move your lips to go thru the various vowels, ooo-aw-aeh-eee, and back again. What you're doing is creating a resonant cavity that emphasizes certain harmonics. When you move your lips, the resonant frequency changes. Eventually you should be able to "tune" to specific harmonics and hear them individually. Say you're singing C below middle C; you should be able to tune your mouth cavity to middle C, middle G, C above middle C, and E an octave and a third above middle C, all while continuing to sing the original pitch. Those are harmonics 2,3,4 and 5. With practice you can sing "taps" on one note. It helps if you sit at the piano and pick out the notes so you know what pitches you're listening for.

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