Re: DBT in audio - a protocol

On 13 Jan 2006 15:11:01 -0800, "andy" <andy19191@xxxxxxxxxx> wrote:

>Don Pearce wrote:
>> No, please try again. I really didn't understand how sighted bias
>> could be factored out of this situation.
>
>Consider an experiment where the subject sees the 4 pairs:
>
> A B, A B, A B, A B
>
>but actually hears the 4 pairs:
>
> A B, B A, A A, B B
>
>If the subject claims to hear (D=different and S=same):
>
> D D D D then 100% correlated with sight and 0% corrleated with
>sound
>
> D D S S then 0% correlated with sight and 100% correlated with
>sound
>
> S S S S then 0% correlated with sight and 0% correlated with
>sound
>
>The first indicates the subject is biased by sight and cannot tell from
>the sound, the second indicates the subject is not biased by sight and
>can tell from the sound and the third is not biased by sight but cannot
>tell from the sound.
>
>Obviously one needs to take more samples to get a reasonable level of
>confidence in the results. The required number of samples will also be
>signficantly more than that required with blind testing for the same
>level of confidence.
>
>As presented, the experiment is also almost certainly too naive to get
>accepted by most subjects. Complexity will need to be added.
>Nonetheless, hopefully, the principle is clear.
>
>A completely different approach for sighted testing could be to
>determine the difference between the two cables and create a modified
>copy of the source so that when played back using one of the cables it
>produces an identical acoustic output (way within what is discernible
>in the room) to that produced using the other cable. This is unlikely
>to be particularly difficult and can be checked with a microphone since
>the room response is not going to be a problem. This would avoid having
>to visually deceive the subject and still allow the subject to hear
>either identical sounds or sounds which differ by the properties of the
>cables. Note that the task of the subject is still the same: to hear an
>unprocessed difference.

You need to think this through a bit. Do you know how unflat the
response of a room is - and how much it varies with even a couple of
millimetres of movement? Likewise for a microphone. What you are
suggesting here could not be done, even in the best anechoic chamber
with the best microphone.

And what do you do about the fact (to 99.9999999% certainty) that
there IS no audible difference between the cables to factor out - what
is it that you are actually adding to the signal here?

d

Pearce Consulting
http://www.pearce.uk.com
.

Relevant Pages

  • Re: DBT in audio - a protocol
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