| Audio Compression Idea [message #84253] |
Thu, 10 May 2007 00:20  |
Kim
Messages: 1246
Registered: October 2005
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Senior Member |
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I'm not sure if I'm missing something here, but if I am I don't see what
it could be. I'm just wondering what the point is of a WAV file given that
they are so big and clunky. I was considering different options for storing
audio. This particular concept is a bit of a mix of the concept of floating
point numbers, mixed with the SA audio format, in combination with some other
ideas. I came to the conclusion that you could store audio in a far better
compressed and lossless format, with infinite amplitude, using far less bits
than standard WAV files, with an end result identical in accuracy to a standard
WAV file except without the amplitude limit.
Programmers amongst you, ponder this for a moment:
Imagine that your audio packets are sequenced in binary like so:
Bit 1: +/- bit - signifies whether the wave is going up or down.
Subsequent data: XY pair where X is a data bit, and Y is the end bit.
....continue with said pattern until an end bit is found.
For example, silence, or any flat signal, would be represented with the sequence
001 repeated. The first zero is the +/- sign (in this case irrelevant as
the data is a zero). The second bit is the signal movement data (0 indicates
the amplitude hasn't moved) and the last bit is the end bit, indicating we
can move on to the next piece of data. This would create a flat line in 3
bits, rather than 16 bits.
If the signal is rising or falling by 45 degrees or less, then we can still
represent it in 3 bits. The 3 bits allows the signal to rise in steps of
a single bit, hence allowing you to map an exact digital path of up to 45
degrees in either direction with three bits instead of 16.
If you go through the math (assuming a 100& value is a straight line directly
up and 0% is directly across):
Rising by 75% would use 5 bits
Rising by 87.5% would use 7 bits.
15 bits would allow a rise/fall of 99.21875%
I can't imagine it would be very often that you would require a rise or fall
of greater than 99.21875%, hence you would always be saving space. Worst
case, a 33 bit message would give you exactly the same ability to rise and
fall as the current 16 bit wav message gets if you go from 0 to 65535 in
one step, but I can't imagine this ever happens in reality. The point is
you could replicate it if required.
You could gain further efficiency from the first two bits by slightly changing
the system. So:
001 = No change
011 = Subtract 1 from value
101 = Add 1 to value
111 = Add 2 to value
By doing this a three bit packet can go anywhere from down 45 degrees, to
up 67.5 degrees. You could gain even more data efficiency by allowing a "change
direction" of the bias in the header packet, so if we had a 1KB number series,
the initial packet would have a bit signifying whether the bias in this packet
was towards up, or down. Using this as a system we could probably reduce
the vast amount of audio down to just 3 bit packets, rather than 16 bit packets.
You would have:
(*) Infinite amplitude to your signal
(*) Lossless compression
(*) Probably 75% or more reduction in data size compared to wav.
You could use near identical technology with video. Each bit of video data
could be represented in 3 bits assuming that they were not changing in value
or were changing slowly, and once again you would have lossless compression.
I have another theory to gain a more analog sound, which I'm still considering,
but I thought I'd throw that one out there. Some comments would be good,
and if somebody with programming nouse would like to throw an encoder/decoder
together, well go for it, so long as the format stays in the public domain.
What do you think? Sound feasible?
Cheers,
Kim.
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