Electronics > Beginners

how do you interpret the raw data of a WAV file?

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engineheat:
I'm trying to do some signal processing on a WAV file. The data is just an array of integers, with some as high as 20000. I believe each data point is 16 bit and I get the concept of bit depth.

But I still struggle to understand the "unit" of that amplitude. I get that amplitude is a measure of the intensity of the sound and that sound is a pressure wave. Is it 20000 what?

Is this number arbitrary? What if I halved all the data by multiplying by 0.5, I frequency spectrum will be the same but the magnitude at the frequencies will be halved as well. Will the sound be half as loud then?

Thanks

ataradov:
It is exactly like you described. It will have half the amplitude, but the spectrum will remain the same. With 16 bits you should see numbers in the range -23768 - 32767.

amyk:

--- Quote from: engineheat on January 09, 2019, 01:06:24 am ---But I still struggle to understand the "unit" of that amplitude. I get that amplitude is a measure of the intensity of the sound and that sound is a pressure wave. Is it 20000 what?
--- End quote ---
Ultimately it's 20000 relative to the maximum input amplitude of the ADC that digitised the file.

engineheat:
So the magnitude of those numbers depends on a DAC, and are unit-less. And for the same DAC, a louder sound will result in greater magnitude, but the "sound" itself is defined by the frequency profile. Is this a way to understand it?

I wonder what will happen if I generate a single sine wave of an audible freq like 5khz, convert it to a WAV file and play it on my computer. I will experiment with this but I'd like to know what to expect now. Maybe playing around with a simple sine wave and listening to the effect will make things clear.

thanks

Psi:
When i was doing this i used cooledit to make a WAV file of silence.
Then i zoomed all the way in and edited a few individual samples. Some up to max, some down to max etc..
Then i used a hex editor to see what was happening in the data and look for the patterns.

It really helped to understand the formatting.

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