Re: Perceivable time differences [was Re: PSA: Clock drift and pkgin]

Ok. I oversimplified.

If I remember right, the point was that something sub 200ms is perceived 
by the brain as being "instananeous" response. It don't mean that one 
cannot discern shorter times, just that from an action-reaction point of 
view, anything below 200ms is "good enough".

My point was merely that I don't believe you need to have something down 
to ms resolution when it comes to human interaction, which was the claim 
I reacted to.

   Johnny

On 2023-12-31 02:47, Mouse wrote:
>> ? If I remember right, anything less than 200ms is immediate response
>> for a human brain.
> 
> "Response"?  For some purposes, it is.  But under the right conditions
> humans can easily discern time deltas in the sub-200ms range.
> 
> I just did a little psychoacoustics experiment on myself.
> 
> First, I generated (44.1kHz) soundfiles containing two single-sample
> ticks separated by N samples for N being 1, 101, 201, 401, 801, and
> going up by 800 from there to 6401, with a second of silence before and
> after (see notes below for the commands used):
> 
> for d in 0 100 200 400 800 1600 2400 3200 4000 4800 5600 6400
> do
> 	(count from 0 to 44100 | sed -e "s/.*/0 0 0 0/"
> 	echo 0 128 0 128
> 	count from 0 to $d | sed -e "s/.*/0 0 0 0/"
> 	echo 0 128 0 128
> 	count from 0 to 44100 | sed -e "s/.*/0 0 0 0/"
> 	) | code-to-char > zz.$d
> done
> 
> I don't know stock NetBSD analogs for count and code-to-char.  count,
> as used here, just counts as the command line indicates; given what
> count's output is piped into, the details don't matter much.
> code-to-char converts numbers 0..255 into single bytes with the same
> values, with non-digits ignored except that they serve to separate
> numbers.  (The time delta between the beginnings of the two ticks is of
> course one more than the number of samples between the two ticks.)
> 
> After listening to them, I picked the 800 and 1600 files and did the
> test.  I grabbed 128 bits from /dev/urandom and used them to play,
> randomly, either one file or the other, letting me guess which one it
> was in each case:
> 
> dd if=/dev/urandom bs=1 count=16 |
>    char-to-code |
>    cvtbase -m8 d b |
>    sed -e 's/./& /g' -e 's/ $//' -e 's/0/800/g' -e 's/1/1600/g' |
>    tr \  \\n |
>    ( exec 3>zz.list 4>zz.guess 5</dev/tty
>      stty -f /dev/tty min 1 time 0 -icanon
>      while read n
>      do
> 	echo $n 1>&3
> 	audioplay -f -c 2 -e slinear_le -P 16 -s 44100 < zz.$n
> 	skipcat 0 1 0<&5 1>&4
>      done
>    )
> 
> char-to-code is the inverse of code-to-char: for each byte of input, it
> produces one line of output containing the ASCII decimal for that
> byte's value, 0..255.  cvtbase -m8 d b converts decimal to binary,
> generating a minimum of 8 "digits" (bits) of output for each input
> number.  skipcat, as used here, has the I/O behaviour of "dd bs=1
> count=1" but without the blather on stderr: it skips no bytes and
> copies one byte, then exits.  (The use of /dev/urandom is to ensure
> that I have no a priori hint which file is being played which time.)
> 
> I then typed "s" when I thought it was a short-gap file and "l" when I
> thought it was a long-gap file.  I got tired of it after 83 data
> samples and killed it.  I then postprocessed zz.guess and compared it
> to zz.list:
> 
> < zz.guess sed -e 's/s/800 /g' -e 's/l/1600 /g' | tr \  \\n | diff -u zz.list -
> 
> I got exactly two wrong out of 83 (and the stats are about evenly
> balanced, 39 short files played and 44 long).  So I think it's fair to
> say that, in the right context (an important caveat!), a time
> difference as short as (1602-802)/44.1=18.14+ milliseconds is clearly
> discernible to me.
> 
> This is, of course, a situation designed to perceive a very small
> difference.  I'm sure there are plenty of contexts in which I would
> fail to notice even 200ms of delay.
> 
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-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
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