On 30.7.2012. 20:51, robert bristow-johnson wrote:
i didn't have anything to do with the subtract-the-moving-average DC block filter.
I apologize...at least I attributed too much rather than too little ;)
if you can put up with delay (which is what you must for a causal and linear-phase filter), you can subtract the moving-average from the sample in the middle of the buffer, not the most current sample.
Well, for a live meter delay is obviously very undesirable. Taking into account the "laziness" of human senses, I guess up to ~5ms might be tolerable, that's about 220 samples@44.1kHz. If the DC filter is placed after the upsampler (as they seem to imply in the standard) and we upsample by a factor of 8 that becomes ~1760 samples...would that be enough for real-world DC offset tracking?
But, more importantly, this might not be needed at all because, as I pointed out in my first mail, "they" (the ITU-R and EBU standard "developers") obviously think/imply that using a plain IIR DC blocking filter is "just fine" (and one would certainly expect the standard not to err in such fundamentals, especially considering the amount of people that worked on it). The question, again, is how (can it be "just fine")? Unless the answer is in the JOS link (the near zero-phase)..?
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