0

I am currently having trouble understanding the significance of negative amplitudes in a traditional Sound Wave, such as in the Short values of Android's Audio Record.

1. Is the amplitude still the distance between zero and the value of the node (absolute value), or the distance from the previous node to the current?

Basically, I am looking into Ludvigsen's Sound Classification Technique (1993), but the demonstrations I have looked in show only positive values.

2. Some Sound Waves have negative values after a previous negative value (or vice versa) rather than bouncing below or above zero after each value. Such as center of image at: http://puu.sh/a0dhg/62b2a5c6da.png (I cannot post images directly yet due to missing reputation).

Therefore my remaining question is: When does a Sound Wave "decide" to go above or below zero? Since I was of the idea the below-zero is sort of a retractions of a previous above-zero value (compression being pushed and bounces back), but moving in the same direction in relevance to zero seems somewhat illogical.

That's pretty much it, thanks in advance. Your help will be most appreciated.

moken
  • 3,227
  • 8
  • 13
  • 23
Joseph Grech
  • 33
  • 7
  • I may be wrong, but this doesn't seem relevant to Stack Overflow, try to relate your question to programming topics. – Luke Joshua Park Jul 07 '14 at 05:43
  • Seems off topic for SO, but potentially a good question on [Physics SE](http://physics.stackexchange.com/). But please don't shout. – paisanco Jul 07 '14 at 05:44
  • Sorry, was trying to keep the question concise since it is already lengthy. But, yes. This is related to programming. Android's AudioRecord / MediaRecorder classes to be exact. The Short Array returned by either has both positive and negative amplitudes, and I have confirmed that these values are are valid since exported and plotted plot the same Graph as a software called Audacity which also plots sound waves from raw data. – Joseph Grech Jul 07 '14 at 05:48
  • @JosephGrech: Then please tag it so in the future. – leppie Jul 07 '14 at 05:49

1 Answers1

0

The amplitude of a wave is a measure for its strength (loudness in case of sound). It basically tells you how far the wave swings away from the neutral position. Several definitions do exist, see for example Wikipedia.

The frequency of the wave is a measure of how often in a second it swings a full period (zero - max value - zero - min value - zero).

Any sound can be thought of a composition of several pure sine (and cosine) waves of different frequencies and amplitudes.

Henry
  • 42,982
  • 7
  • 68
  • 84
  • Thanks, your answer has helped a bit. If I may ask you a more specific question regarding your "The frequency of the wave is a measure of how often in a second it swings a full period (zero - max value - zero - min value - zero)." ... Occasionally my sound does not go back to zero, only goes slightly towards it and then back down/up. These are occurrences which are slightly confusing. (As per the screenshot in the link in my original question) – Joseph Grech Jul 07 '14 at 06:46
  • @JosephGrech That's because what you see in practice is almost always a mixture of several frequencies. For example a low frequency component combined with a smaller higher frequency component would have a similar behaviour. See for example here: http://en.wikipedia.org/wiki/Continuous_Fourier_transform – Henry Jul 07 '14 at 10:21