Wednesday, December 20, 2006

Noise Floor? What Noise Floor?

For my performance review I thought it would be interesting to compare the self-noise of the electret capsules. I had noticed that the SoundProject Omni's had a slight buzz when I listened closely, so I wondered if there was any such subtle signature sound for each of the capsules. As it turned out, given the "test environment" of the Pieper warehouse, I could scarcely tell the recordings apart. But, just for fun and because I thought we needed another pretty picture on this site, I ran off a comparison sonogram of the four capsule mics side-by-side. It was produced from this recording (Test 5) which shares the same left to right order as the picture (Primo, Shure, SoundPro, Rapid).

In the sonogram, the purple-blues are the loudest frequencies and the yellow-whites are the softest. As the image contests, my ears weren't fooling me - in the droning hum of the warehouse, these capsules sounded practically the same. Any subtle differences might be attributed to the different rigs (headphone, parallel boundary) that these mics were mounted in. There are some small distinctions between the mics in the low freqency range (the fat blue bands) that may indicate that the Primo and SoundPro were a little bit quieter, but if one were to really want to test the noise levels of these mics, It might be best to find an anechoic chamber.

Brennan Alcott

added later:
Rob D's linear sonogram at -90dB to 24K:

click on picture to enlarge

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.

Padrick Dunns: localization Test

For localization I selected six different test rigs. They are tested in groups of
two. Starting with:

13'' spread side-facing capsules w/baffle Em 158 and 21'' spread side facing capsule w/baffle

T01-01 and T03-01

I listened to each one about six time while I drew a circle and placed each mark so I could localize each mark. This goes for all of the tests. At first I did it looking at the computer but it took my attention away from where the sound was really coming from. When I closed my eyes I came up with this conclusion. Starting with the T01-01 13'' spread the separation of the sound was much more clear than the 21'' spread this could be because ot the piece of cardboard in the middle. It seemed that the variation is much different from the T010-01 to the T03-01. The sound from T01-01 has separation and you can tell where each sound is coming from where the sound from T03-01 10-12 degrees is way off they sound like their are on top of each other. Where 12-1 their is a large seperation. In conclusion the sound is much more clear when the mics are closer together in this case.

The next two are:

Front-facing w/Baffle 13'' spread em158 and Front-facing w/baffle 21'' spread em158 mics

T01-02 and T03-02

Starting with the T01-02 13'' spread 12-1 sounded right next to each other but 11-12 sounded like there was a large amount of separation. Where in the T03-02 10-11 sounded right next to each other. 12-2 also sounded on top of each other. Each group had its separations but it seems that the closer the mics are together the better the localization of each sound.

The next two are:

13''spread ORTF Em 158 mics baffle and 21'' spread ORTF Em 158 mics baffle

T01-03 and T03-03

The most interesting group was the last only becaule it was different from the first two. As I started with the T01-03 the degree of 10-12 sounded right next to each other as well as the 12-2. It seems that this was the worst test for localization. It was hard to distinguish between the degrees of 10 and 12, also 12 and 2. Then I shifted gears and listened to the T 03-03. The further the spread in teh ORTF baffle the better the separation of the sound. The localizaton was much better and much more clear. In conclusion the further the mic the better the localization in the ORTF.


If I could pic one mic out of the six for localization it would be the 21'' spread ORTF Em 158 mics baffle. If I could pic a second runner up it would be the 13'' spread side facing capsules w/baffle Em 158. I found it weird that the closer the side facing baffle the better the sound quality and the further apart the ORTF the better the sound quality.