Solving Audio Sources Doubt - Devanand T

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Discussion Overview

The discussion revolves around the nature of audio perception when multiple sound sources are present, specifically focusing on how the ear and brain process overlapping audio signals, such as music from a CD player and speech from a radio. The conversation touches on the mathematical operations involved in sound signal processing and the auditory experience.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Devanand T questions whether the resultant audio signal heard from two sources is a simple addition of the signals or involves a different operation.
  • One participant explains that the ear and brain can separate signals based on direction and frequency content, allowing for the perception of multiple sources even when mixed.
  • Another participant agrees with the idea of superposition, stating that the sound pressure waves reaching the ear represent a single sound that is the sum of all signals, influenced by their phase and amplitude.
  • The concept of comb filtering is introduced, where two sounds can interfere with each other depending on their phase, affecting how they are perceived.
  • A mention of beats occurring when two sine waves of close frequencies are played together, illustrating another aspect of sound interaction.

Areas of Agreement / Disagreement

Participants express varying views on how audio signals are processed and perceived, with some agreeing on the superposition concept while others introduce additional complexities like comb filtering and beats. The discussion remains unresolved regarding the exact nature of the resultant audio signal.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about sound processing and the definitions of terms like superposition and comb filtering, which may not be universally understood.

Who May Find This Useful

Individuals interested in audio engineering, signal processing, and the psychology of sound perception may find this discussion relevant.

dexterdev
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Audio sources doubt...

hi all,
I don't know where to post this. sorry for that.

My doubt is that if there are 2 audio sources like one mp3 music file playing from a cd player and another speech signal coming from a radio. If I can hear both signals, what is the resultant audio signal which my ear hears. Does the mathematical operation done is addition of those signals and then hear it as a single sound or any other operation.

- Devanand T
 
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The ears (together with the brain) form a very sophisticated detector. You can easily separate signals based on their different originating directions, so you would be recognizing two different sources. Even were you to mix the signals so that they originated from the same location, your brain can readily separate them based on the different levels/frequency spectrum/content, etc., so again you would be hearing two different sources. (That explains why you can make out the words someone is speaking at a party, even when there are many other voices, some louder, all around.)

Maybe you could record one track of a musical hit on a CD, and another track of the same music on an mp3, and then play these synchronized and originating from the same point in a room. Then you may succeed in having the ears believe they are hearing only one source, that being the sum of those two.

The ears themselves sense the sum of the two signals; it's the brain that takes credit for performing all the complex processing, of course.
 


dexterdev said:
hi all,
I don't know where to post this. sorry for that.

My doubt is that if there are 2 audio sources like one mp3 music file playing from a cd player and another speech signal coming from a radio. If I can hear both signals, what is the resultant audio signal which my ear hears. Does the mathematical operation done is addition of those signals and then hear it as a single sound or any other operation.

- Devanand T

The sound pressure waves into your ears are a single sound, and it is the superposition (like you said, it is addition) of all of the different sounds at any instant that they are arriving at your ear. With respect to NascentOxygen's post, the superposition coming in will be dependent on the phase and amplitude of each individual sound signal, and so there is still information that let's your brain/signal processor tell the difference between the sounds.

An interesting effect of this is comb filtering, where 2 sounds can add together at your ear, and, depending on where they came from, they can interfere with each other (they are out of phase). I think audio technicians and producers can use this to optimize their recording studios.
http://en.wikipedia.org/wiki/Comb_filter

A field of signal processing takes advantage of this comb filter effect in something called the cepstrum.
 
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When you have two sine waves with frequencies that are close together, you can hear what's know as beats.

beatsmall.gif


By varying the difference between these tones, you can vary the "beat frequency". Here are some animations with sound to see how this works.

Interference beats and Tartini tones
 


thanks for the replies guys
 

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