At 9:58 AM -0700 7/27/10, Dan Dugan wrote:
>
>
> >>>> I suggest that boundary array experimenters set up their rigs
>>>>> outdoors, listen to just one channel on both ears,
>>>>
>>>> ? Can you clarify this part?
>>>
>>> Listen to just the left or right mic with both ears, to put stereo
>>> effects out of the picture.
>>>
>>> -Dan
>>>
>> Here's a blind comparison movie created from the results of a moving
>> pink noise test that is hopefully very similar to what Dan suggested.
>> The (3mb .zip) download link is at the bottom of the blog post here:
> > <http://tinyurl.com/2egg33s>http://tinyurl.com/2egg33s Play it
>with QuickTime or a
>> QuickTime-compatible player on your computer.
>
>Very nice, thank you, Rob.
>
>I've posted a Spectrafoo sonogram of the MP3 at:
>
><http://www.dandugan.com/downloads/Miscellany/20100726_BoundaryCombFilteri=
ng.png>http://www.dandugan.com/downloads/Miscellany/20100726_BoundaryCombFi=
ltering.png
>
>and another with higher gain trying to show the highest frequencies better
>
><http://www.dandugan.com/downloads/Miscellany/20100726_BoundaryCombFilteri=
ng_2.png>http://www.dandugan.com/downloads/Miscellany/20100726_BoundaryComb=
Filtering_2.png
>
>The most audible effects I hear are a descending tonal effect in the
>mid-range and the directivity of the mics at high frequencies (HF
>comes up as pan comes on axis). Both happen on all three mountings.
>I don't understand the source of the mid-range effect.
>
>Comb filtering effects at the top end that were my concern when I
>proposed the test are more subtle than I expected. I found it useful
>to high-pass the playback way up like 5k-8K to eliminate the
>distractions of the lower effects.
>
>-Dan
>
Hi Dan--
Both files I posted are full res (movie's soundtrack 16/48K and .wav
24/48K). So no mp3 artifacts should be involved.
I'm noticing a dropping chord with a fundamental around 407 Hz that
changes to about 347 Hz in all samples. It sounds a bit like a
Doppler effect but that doesn't seem possible as the speaker isn't
getting closer and the velocities are so low. Could it be something
like a difference tone created by sliding pitch changes high in the
spectrum? Yet, that would be psychoacoustic and there may be a faint
trace of the 407- 347 Hz drop in the sonograms.
Can one tell if the steep, downward sloped bands in the last 2/3rds
of the A samples and the less steep upwards sloped bands in the last
half of C samples is comb filtering? My older ears are pressed to
detect this HF content . Rob D.
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