Robert Oschler wrote:
> Hello again,
> 
> It's me the novice DSP'er who would be king..  er.. frog? :)
> 
> I want to tell when a sound source is "pointing" towards a microphone.  The
> sound source is mobile, but I have complete control over its movement and
> sound emission.  I can easily play repeatedly a pre-recorded sound from the
> sound source, which will be identical every time it's played.  Obviously, it
> will not be identical when picked up by the microphone due to room
> reflection, volume roll-off, distance from the microphone, etc.
> 
> I know that I can have it spin in a circle and do a simple volume level
> check for the point of max volume, but I'd like to back that up with a
> secondary test.  My reasoning is, if the sound source is far from the
> microphone in a highly reflective room, let's say about 10 feet or so, the
> volume differential between dead forward and not, may be too fragile a
> measure.
> 
> So is there a frequency or echo test I can do as a secondary judgement?  I'm
> guessing that there should be a noticeable drop-off in highs as the sound
> source turns away from the microphone.  Are there any cone of projection
> equations that predict what the drop-of would be, which I can use as a test?
> Or perhaps something that can take a sound wave and return a value
> indicating the relative strength of the sound wave to it's own
> echo/reverberation level?  I do have reference waveforms (sound files) of
> the sound that the sound source emits, which I can use for any signal
> processing measures.
> 
> Any ideas?  They don't have to work perfectly, I just want to improve my
> guesses.
> 
> Thanks.
> 
> 

Hmm, what about doing some correlation to determine direct path and
reflections and comparing the magnitude of the direct path with the
magnitude of the first reflection. Maximise the ratio...

Kind regards,

Iwo

Jerry Avins wrote:
> Robert Oschler wrote:
> > Hello again,
> >
> > It's me the novice DSP'er who would be king..  er.. frog? :)
> >
> > I want to tell when a sound source is "pointing" towards a
microphone.  The
> > sound source is mobile, but I have complete control over its
movement and
> > sound emission.  I can easily play repeatedly a pre-recorded sound
from the
> > sound source, which will be identical every time it's played.
Obviously, it
> > will not be identical when picked up by the microphone due to room
> > reflection, volume roll-off, distance from the microphone, etc.
> >
> > I know that I can have it spin in a circle and do a simple volume
level
> > check for the point of max volume, but I'd like to back that up
with a
> > secondary test.  My reasoning is, if the sound source is far from
the
> > microphone in a highly reflective room, let's say about 10 feet or
so, the
> > volume differential between dead forward and not, may be too
fragile a
> > measure.
> >
> > So is there a frequency or echo test I can do as a secondary
judgement?  I'm
> > guessing that there should be a noticeable drop-off in highs as the
sound
> > source turns away from the microphone.  Are there any cone of
projection
> > equations that predict what the drop-of would be, which I can use
as a test?
> > Or perhaps something that can take a sound wave and return a value
> > indicating the relative strength of the sound wave to it's own
> > echo/reverberation level?  I do have reference waveforms (sound
files) of
> > the sound that the sound source emits, which I can use for any
signal
> > processing measures.
> >
> > Any ideas?  They don't have to work perfectly, I just want to
improve my
> > guesses.
> >
> > Thanks.
>
> Your quest is hopeless without some knowledge of the (possibly
> frequency-dependent) radiation pattern of the source. It could be
easy
> to determine that a large-mouth horn or parabolic reflector is
pointed
> right at the receiver, especially it impulsive transients make it
> possible to detect and discount reflections. With an isotropic
radiator,
> a directional microphone can determine its direction but not its
> orientation. With a cardioid pattern, you might be able to determine
if
> the receiver is near its null, but any other azimuth becomes
> problematic. With the relatively common figure-eight pattern, there
is a
> 180 degree ambiguity whatever scheme is adopted.

Agreed. And the internal sound patterns of the room don't help.

This problem is well-known from video conference applications, where
one wants the microphone array to focus on the current speaker,
whereever
he or she is in the room, and reject everything else. At fist glance,
it
seems to be a beamforming problem, but being in a room obfuscates
things.

I don't know if anyone have managed to solve this problem.

Rune

"Robert Oschler" <no-mail-please@nospam.com> wrote in message 
news:Kv6dnTqIPcO0hP_fRVn-jA@adelphia.com...
> Hello again,
>
> It's me the novice DSP'er who would be king..  er.. frog? :)
>
> I want to tell when a sound source is "pointing" towards a microphone. 
> The
> sound source is mobile, but I have complete control over its movement and
> sound emission.  I can easily play repeatedly a pre-recorded sound from 
> the
> sound source, which will be identical every time it's played.  Obviously, 
> it
> will not be identical when picked up by the microphone due to room
> reflection, volume roll-off, distance from the microphone, etc.
>
> I know that I can have it spin in a circle and do a simple volume level
> check for the point of max volume, but I'd like to back that up with a
> secondary test.  My reasoning is, if the sound source is far from the
> microphone in a highly reflective room, let's say about 10 feet or so, the
> volume differential between dead forward and not, may be too fragile a
> measure.
>
> So is there a frequency or echo test I can do as a secondary judgement? 
> I'm
> guessing that there should be a noticeable drop-off in highs as the sound
> source turns away from the microphone.  Are there any cone of projection
> equations that predict what the drop-of would be, which I can use as a 
> test?
> Or perhaps something that can take a sound wave and return a value
> indicating the relative strength of the sound wave to it's own
> echo/reverberation level?  I do have reference waveforms (sound files) of
> the sound that the sound source emits, which I can use for any signal
> processing measures.
>
> Any ideas?  They don't have to work perfectly, I just want to improve my
> guesses.
>
> Thanks.
>
>
Hi Robert,
The most directional microphone you can find would help in most situations 
where you know where the soound source is but don't know which way its 
pointing. Other than that I can only suggest you record the sound in a fair 
sized window. Normalise to the total power or peak power in one of the 
stronger frequencies if background noise is a consideration and then 
determine arrival time of the next transmissions by correlation. If you set 
it up so it transmits at regular intervals and then compare the times 
between the first echos in each recorded interval you could maybe decide 
which positions are not actually echos at all but direct path. After that 
things get tricky ; I'd compare the energy in the "first echo" window for 
all of your transmissions and guess that the highest amplitude was with the 
source pointing most directly towards you.  I've no idea how cheap and 
cheerful this is - best of Luck - Mike

Robert Oschler wrote:
> Hello again,
> 
> It's me the novice DSP'er who would be king..  er.. frog? :)
> 
> I want to tell when a sound source is "pointing" towards a microphone.  The
> sound source is mobile, but I have complete control over its movement and
> sound emission.  I can easily play repeatedly a pre-recorded sound from the
> sound source, which will be identical every time it's played.  Obviously, it
> will not be identical when picked up by the microphone due to room
> reflection, volume roll-off, distance from the microphone, etc.
> 
> I know that I can have it spin in a circle and do a simple volume level
> check for the point of max volume, but I'd like to back that up with a
> secondary test.  My reasoning is, if the sound source is far from the
> microphone in a highly reflective room, let's say about 10 feet or so, the
> volume differential between dead forward and not, may be too fragile a
> measure.
> 
> So is there a frequency or echo test I can do as a secondary judgement?  I'm
> guessing that there should be a noticeable drop-off in highs as the sound
> source turns away from the microphone.  Are there any cone of projection
> equations that predict what the drop-of would be, which I can use as a test?
> Or perhaps something that can take a sound wave and return a value
> indicating the relative strength of the sound wave to it's own
> echo/reverberation level?  I do have reference waveforms (sound files) of
> the sound that the sound source emits, which I can use for any signal
> processing measures.
> 
> Any ideas?  They don't have to work perfectly, I just want to improve my
> guesses.
> 
> Thanks.

Your quest is hopeless without some knowledge of the (possibly 
frequency-dependent) radiation pattern of the source. It could be easy 
to determine that a large-mouth horn or parabolic reflector is pointed 
right at the receiver, especially it impulsive transients make it 
possible to detect and discount reflections. With an isotropic radiator, 
a directional microphone can determine its direction but not its 
orientation. With a cardioid pattern, you might be able to determine if 
the receiver is near its null, but any other azimuth becomes 
problematic. With the relatively common figure-eight pattern, there is a 
180 degree ambiguity whatever scheme is adopted.

I suspect that the problem is more easily solved with a video camera and 
image analysis.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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Robert Oschler wrote:

> Hello again,
> 
> It's me the novice DSP'er who would be king..  er.. frog? :)
> 
> I want to tell when a sound source is "pointing" towards a microphone.  The
> sound source is mobile, but I have complete control over its movement and
> sound emission.  I can easily play repeatedly a pre-recorded sound from the
> sound source, which will be identical every time it's played.  Obviously, it
> will not be identical when picked up by the microphone due to room
> reflection, volume roll-off, distance from the microphone, etc.
> 
> I know that I can have it spin in a circle and do a simple volume level
> check for the point of max volume, but I'd like to back that up with a
> secondary test.  My reasoning is, if the sound source is far from the
> microphone in a highly reflective room, let's say about 10 feet or so, the
> volume differential between dead forward and not, may be too fragile a
> measure.
> 
> So is there a frequency or echo test I can do as a secondary judgement?  I'm
> guessing that there should be a noticeable drop-off in highs as the sound
> source turns away from the microphone.  Are there any cone of projection
> equations that predict what the drop-of would be, which I can use as a test?
> Or perhaps something that can take a sound wave and return a value
> indicating the relative strength of the sound wave to it's own
> echo/reverberation level?  I do have reference waveforms (sound files) of
> the sound that the sound source emits, which I can use for any signal
> processing measures.
> 
> Any ideas?  They don't have to work perfectly, I just want to improve my
> guesses.
> 
> Thanks.
> 
> 


I think you need to specify how your procedure would eventually be used.

I'm very familiar with one auditorium that would probably drive such a 
program nuts ;) Our church auditorium was designed for preaching 
services in days before electronic amplification was the norm. The wall 
behind podium is curved in such a way to assist the speaker. HOWEVER, if 
one speaks from location other than podium, strange effects occur ;} 
Originally the auditorium was originally VERY LIVE -- we've carpeted the 
walls to allow it to coexist with a sound system.

I would not be _surprised_ [for the unamplified case] that there _may_ 
be speaker locations &/or orientations for which some hearers would hear 
better when speaker was facing away.

Robert Oschler wrote:
> I want to tell when a sound source is "pointing" towards a
microphone.  The
> sound source is mobile, but I have complete control over its movement
and
> sound emission.  I can easily play repeatedly a pre-recorded sound
from the
> sound source, which will be identical every time it's played.
Obviously, it
> will not be identical when picked up by the microphone due to room
> reflection, volume roll-off, distance from the microphone, etc.
>
> I know that I can have it spin in a circle and do a simple volume
level
> check for the point of max volume, but I'd like to back that up with
a
> secondary test.  My reasoning is, if the sound source is far from the
> microphone in a highly reflective room, let's say about 10 feet or
so, the
> volume differential between dead forward and not, may be too fragile
a
> measure.


If you want to test different methods, one springs to my mind:
Say the emitted sound is x(t) and the received one is y(t). Then
compute the correlation signal of x and y. The first peak (and
probably highest, but not necessarily) in the correlation will
be due to line-of-sight transmission, while other peaks must come
from echoes. You can suppose (you might be wrong, it all depends
on room acoustics) that you'll get the highest peak when the
source is "pointing" directly at the microphone.

This is a rather slow task, and not very easy to code. If you
choose to do it, I suggest that you employ a chirp signal, since
it behaves very well with respect to correlation.

In any case, I don't think there is a reliable way of doing what
you want, unless you know well the source's emission diagram and
the acoustics of the room.

Hello again,

It's me the novice DSP'er who would be king..  er.. frog? :)

I want to tell when a sound source is "pointing" towards a microphone.  The
sound source is mobile, but I have complete control over its movement and
sound emission.  I can easily play repeatedly a pre-recorded sound from the
sound source, which will be identical every time it's played.  Obviously, it
will not be identical when picked up by the microphone due to room
reflection, volume roll-off, distance from the microphone, etc.

I know that I can have it spin in a circle and do a simple volume level
check for the point of max volume, but I'd like to back that up with a
secondary test.  My reasoning is, if the sound source is far from the
microphone in a highly reflective room, let's say about 10 feet or so, the
volume differential between dead forward and not, may be too fragile a
measure.

So is there a frequency or echo test I can do as a secondary judgement?  I'm
guessing that there should be a noticeable drop-off in highs as the sound
source turns away from the microphone.  Are there any cone of projection
equations that predict what the drop-of would be, which I can use as a test?
Or perhaps something that can take a sound wave and return a value
indicating the relative strength of the sound wave to it's own
echo/reverberation level?  I do have reference waveforms (sound files) of
the sound that the sound source emits, which I can use for any signal
processing measures.

Any ideas?  They don't have to work perfectly, I just want to improve my
guesses.

Thanks.