Subject: [clue] Add an attribute for sensitivity pattern of microphones

From: John Leslie <[email-masked]>
Date: Mon, 12 May 2014 07:06:16 -0400

Actual microphones are never equally sensitive in every direction.
So-called "omnidirectional" microphones are noticeably less sensitive
to sounds 90 degrees off-axis. This sensitivity also varies with
frequency.

   "Cardioid" microphones have a pronounced null 180 degrees off-axis.
There are also "shotgun" microphones and "noise-cancelling" microphones
which have pronounced patterns.

   Not every sound engineer will want to reveal which kind of
microphone is being used for each pickup point (or, perhaps, even
know the difference). But sensitivity pattern is needed to fully
describe individual microphone media streams. Thus I recommend
adding an element for audioCapturePattern to the audioCaptureType:
an enumeration value, initially "generic omnidirectional",
"generic cardioid", and "unknown". There will be a need to expand
the possible values, and I propose an IANA registry
first-come-first-served.

--
John Leslie <[email-masked]>

---

From: Paul Coverdale <[email-masked]>
Date: Mon, 12 May 2014 11:39:19 -0400

>-----Original Message-----
>From: clue [mailto:[email-masked]] On Behalf Of John Leslie
>Sent: Monday, May 12, 2014 7:06 AM
>To: [email-masked]
>Subject: [clue] Add an attribute for sensitivity pattern of microphones
>
>So-called "omnidirectional" microphones are noticeably less sensitive to
>sounds 90 degrees off-axis. This sensitivity also varies with frequency.

[Paul Coverdale] I guess you're referring to the free-field correction. If
so, it's only noticeable at high frequencies, and depends on the microphone
size. But I agree with the notion that a given "ideal" microphone pattern
will not necessarily be achieved in practice, so the use of the term
"generic" is more appropriate.

>   Not every sound engineer will want to reveal which kind of microphone
>is being used for each pickup point (or, perhaps, even know the
>difference). But sensitivity pattern is needed to fully describe
>individual microphone media streams. Thus I recommend adding an element
>for audioCapturePattern to the audioCaptureType:
>an enumeration value, initially "generic omnidirectional", "generic
>cardioid", and "unknown". There will be a need to expand the possible
>values, and I propose an IANA registry first-come-first-served.

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