Wednesday, December 20, 2006

Reflected Sound and Variance (Matthew Engel)

T05 Comparative
The measurement of traveling sound towards two different mics from the same sound source is an interesting way to identify and map out the space used in these recordings. The differences in pitch and overall reception of the sound in the two different mics is interesting because it gives a lot of information about how sound is traveling in this space and how it reflects off certain surfaces to reach the mic locations in the center. To lift a diagram, earlier used by Anthony, this is a good reference of the types of ways mics and mic rigs receive and develop certain sound receptions to create what we hear in much of these recordings, however its more important that we pay close attention to the first image because it defines what is being talked about here. It is a graphic depiction of how direct sound and reflected sound reach the mics from the points in the Pieper barn that we were using.
Using information from Test five, I was able to determine a certain amount of variances and sound differences in the way the sound is received by two similar sources in two different positions. These positions do affect the final out come of the sound reception, but it is easy to determine the difference in the decay of the sound in each. The two different sounds from the points 10 and 2, chosen for their placements in cramped and open spaces, create a totally different sound from the one mic setup to the next. This is because of placement of the mics, the mic quality, the space surrounding the sound source, and the recording circumstances such as gain level. But the most interesting aspect to try and decipher from the recordings is the space around the sound source. This space is important because it is the reflected surface of the sound being produced and it is what creates the spatial anomalies and produces the amount of ambiance in the sound itself to let our ears hear that there is resonance and large or small amount of space surrounding the sound source. These two recordings both being done by types of parallel boundary mic rigs, this comparison develops a greater idea of the recording space then by just listening to one individual recording, and this is attributed to the ambient reception difference in each of the two different mics at their different positions.
To get down to it, the variance of space in point 10 is less because it has an almost immediate reflected sound where as point 2 has a more muted and less active sound because it is in the area of the barn with the most space. The tests have been placed here side by side to see for yourself. They are played at 25% slower speeds in the first set, and then normal the second set. The major differences in sound captured in the slowed down versions are very obvious and represent the variances in spatial reflection rather well. Keeping all the other elemental controls and effects in mind, see if you can hear the reflections and differences caused by this very cold space.

1 comment:

us said...

Hi Matt--

So, with two similar but not exact parallel boundary rigs and two different mics and the same sound stimuli, can one hear that the rigs are in different two different places? This is a great practical question to ask about rig performance isn't it?!

I agree with you that, "yes" I can and, "yes," the left side impulses are harder to discern than the right side (which has been suggested by other tests too).

Good job. The goals of your test could be stated more clearly. A map of the two mic station locations in the space would have really helped. The distances between the rigs and to the sound sources and estimates to the walls-- all are critical for someone who hasn't been to the space.

I was able to use mental imaging to conduct the test. The speed changes were unnecessary, thougn curious. I could tell, for example, that the 10 strike edged closer to the 11 "in mental appearance" with the rig on the centerline and more towards the 9 with the rig to the right of the center ine and closer to the front.

For some reason, the video format you uploaded was giving all of my players the fits (even when downloaded) or I would be able to make more detailed response to your assessment. I provided a link to quicktime file export instructions. If you followed these and ended-up with the results posted here, let me know. One needs to be confident that one can make and upload movies that will play for almost anyone.

Another conclusion is, the parallel boundary rigs can define a shift in location of about 10 feet in the left-right axis without problem even though different sounding large and small diameter omni-directional mics were used. Rob D.