[mvsainz]

Hi there guys!

I'm Marco, from Miami. Still new in the "audiophile" world, but hey, it's one step at a time. I did have one question that's bugging me though. A technical one.

I get the idea of bit rate and bit depth, but one thing I don't seem to quite find an answer to is how music is reproduced. My question is, are various frequencies reproduced simultaneously, or individually, and how are they played. What this means in plain english is, if I, lets say, if you have a recording of a low frequency drum and a high pitched flute at the same time, It's easy to imagine that the frequency graph would show a peak at the lows and the highs. But my question is, does a headphone reproduce simultaneously both frequencies at the same time, or does it "sum them up" for the lack of a better turn, and play the combination of both frequencies?

And when one says something like 24bit 192kHZ, that means that you divide time in 192k sections, and take measurements off of a fraction of 24 bit combinations, more or less. But again the same question, does it take a measurement of each frequency for each sample period, or does it take a measurement of the "sum"?

That's probably not all my questions, but for now it'll have to be enough. I hope that I'm not the only person with doubts about this. Anyways, thanks and nice meeting you all! Now I'll get back to enjoying my Hifiman HE-400 with my new DIY cable (I'll try to get a couple pics up since I'm trying various designs) and my Ibasso DX50. I'm still in awe from the binaural effects from "Dr. Chesky's Ultimate Headphone Demonstration Disc"!

 

[Pirakaphile]

The drivers in the headphone are making every sound you hear at exactly the same time. Anything above the bass notes are vibrating on top of the lowest notes, so if you could slow down a driver that was playing some absurd bass, you would see the driver moving up and down very slowly, but also moving up and down on a much smaller scale moving faster, for the higher notes.
A headphone itself can't sum anything up, since it's job is to move when it's electrically charged. The only thing in control of the sound is the chip processing the electric signals of the music. I'm getting in way over my brain power, but I tend just to stick with how things sound, rather than getting too technical. Music is about the emotion it carries, not the movement of the speaker.

 

[mvsainz]

Thanks for the description! So the various frequencies of music reproduces by the driver are produced simultaneously. I guess I still don't totally imagine how that's happening, but hey, it's a step in the right dirrection. Maybe I will look into a slow motion video of a speaker to see if that gives insight . I'm a mechanical engineering student, so I guess it would be the wrong career choice if I wasn't interested in how that was happening .

 

[RRod]

Thanks for the description! So the various frequencies of music reproduces by the driver are produced simultaneously. I guess I still don't totally imagine how that's happening, but hey, it's a step in the right dirrection. Maybe I will look into a slow motion video of a speaker to see if that gives insight

. I'm a mechanical engineering student, so I guess it would be the wrong career choice if I wasn't interested in how that was happening

.

 
Think of it this way:
.For a single, fixed frequency, the cone must complete an in/out cycle in a constant amount of time. The only thing that can change is how far in and out it goes, making the sound louder or softer.
.For a fixed amplitude, the cone must move the same distance in and out. The only thing that can change is how quickly it does this, making the sound higher or lower.
 
To handle multiple frequencies at multiple amplitudes (pretty much all natural waves), the cone does a mixture of these two extremes. So instead of moving in/out a constant distance, it can stop half way and move back again. Instead of moving at a constant in/out pace, it can slow down and speed up.

 

[billybob_jcv]

http://www.eetimes.com/document.asp?doc_id=1274799

At each instant in time, the voltage the speaker driver sees is the sum of all frequencies present in the signal. So, if you look at the signal in the "time domain", for a simple case of 1 frequency and then two frequencies, you would get something like this:




The speaker driver responds to voltage - the more voltage, the farther the voice coil moves the diaphragm. The farther the diaphragm moves, the more air it moves and the louder the sound. That's why sound loudness is called the "Sound Pressure Level" (SPL) - the higher the pressure of the sound on your ear drums, the louder it will be. Sound is NOT digital, it is analog, so you can't look at just one instant in time and determine all the frequencies that are present in the signal. You have to look at the signal in a variety of domains, not just the time domain. We approximate the true analog sound by converting it into digital data. That allows us to store it as 1s & 0s instead of as grooves in a piece of wax (an album) or as iron filings on a piece of plastic tape (8-track, cassette or reel-to-reel). We then convert the digital data back into an analog signal so we can send the signal to the speaker driver and ultimately to our ear drums.

 

[MindsMirror]

The previous post is a good example of how multiple frequencies are created at once in the audio. I think a better example that could demonstrate the same idea more obviously would be to look at a signal where the frequencies are further apart.
 
Enter this in google search: 
     sin(2*pi*x) + 0.3*sin(2*pi*10*x) = 
 
It will show you the graph of a signal with a 1Hz plus a 10Hz frequency (with different amplitudes). You can clearly see the two frequencies that exist simultaneously in the signal.
 
A sound file would store the value of the points along the line in that graph, not the value of each frequency.

 

[mvsainz]

Thanks so much for the responses. I finally feel like I got the answer that I was looking for. For some reason I never got emailed regarding the last responses, and they were actually the most enlightening. So thanks a lot for those. Particularly the graph from MindsMirror. Also, I stumbled on an animation of how speakers work, with the graph of the function reproduced included which really answered my question. Just like the formula from the forum, really. In any case, I found it an interesting quick read even if you already have an idea of how it works.
 
http://animagraffs.com/loudspeaker/
 
So thanks guys!