Convert 16 bit pcm to 8 bit

java algorithm audio bit pcm
gop picture gop · Apr 19, 2011 · Viewed 12k times · Source

I have pcm audio stored in a byte array. It is 16 bits per sample. I want to make it 8 bit per sample audio.

Can anyone suggest a good algorithm to do that?

I haven't mentioned the bitrate because I think it isn't important for the algorithm - right?

Answer

unwind picture unwind · Apr 19, 2011

I can't see right now why it's not enough to just take the upper byte, i.e. discard the lower 8 bits of each sample.

That of course assumes that the samples are linear; if they're not then maybe you need to do something to linearize them before dropping bits.

short sixteenBit = 0xfeed;
byte eightBit = sixteenBit >> 8;
// eightBit is now 0xfe.

As suggested by AShelly in a comment, it might be a good idea to round, i.e. add 1 if the byte we're discarding is higher than half its maximum:

eightBit += eightBit < 0xff && ((sixteenBit & 0xff) > 0x80);

The test against 0xff implements clamping, so we don't risk adding 1 to 0xff and wrapping that to 0x00 which would be bad.

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