🚀 go-pugleaf

I can't understand the difference between "spectrum analysis" and
finding "Fourier components".
Ear as a resonator changes Fourier spectrum quite a lot, in particular shifting
cutoff frequencies.
Michael.

philo@athena.mit.edu (philo) writes:

>in my wave mechanics class, we had an accoustics researcher come in as a guest
>lecturer once. One of the things that he said was that a spectrum analysis of the
>speach right near the ear of the listener did not agree with the spectrum of the
>sound as it left the mouth of the person who is talking. However, the fourrier
>components agreed to a large degree.

>Does any one have a better understanding of this concept that I do? I think
>this could be a very interesting question.

He may have been referring to near-field components of the source which would 
not radiate as efficiently or he may have meant to emphasise the fact
the power spectrum contains no phase information. Or something else?

Matthew Wright
Institute of Sound and Vibration Research

In article <1992Nov17.012614.20277@athena.mit.edu> philo@athena.mit.edu (philo) writes:
>lecturer once. One of the things that he said was that a spectrum analysis of the
>speach right near the ear of the listener did not agree with the spectrum of the
>sound as it left the mouth of the person who is talking. However, the fourrier
>components agreed to a large degree.
>
>Does any one have a better understanding of this concept that I do? I think
>this could be a very interesting question.
>-philo.
>dakhlak.... hawn nazl s suruur?
>				(Ziad)


Unless you were in an anechoic chamber, the reverberent field will always
change the frequency content of any acoustic signal.  High frequencies will
be attenuated by the air in the path from source to ear.  Also, the microphone
used to get the acoustic signal into the Fourier analyzer has a non-flat
frequency response.

I am ignoring the fact that FFT's done on non-infinite (in time) signals are
suspect in their validity.

Galen Watts

In article <Nov17.153055.54833@yuma.ACNS.ColoState.EDU> gw214790@LANCE.ColoState.Edu (Galen Watts) writes:
>In article <1992Nov17.012614.20277@athena.mit.edu> philo@athena.mit.edu (philo) writes:
>>lecturer once. One of the things that he said was that a spectrum analysis of the
>>speach right near the ear of the listener did not agree with the spectrum of the
>>sound as it left the mouth of the person who is talking. However, the fourrier
>>components agreed to a large degree.
>>
>>Does any one have a better understanding of this concept that I do? I think
>>this could be a very interesting question.
>>-philo.
>>dakhlak.... hawn nazl s suruur?
>>				(Ziad)
>
>
>Unless you were in an anechoic chamber, the reverberent field will always
>change the frequency content of any acoustic signal.  High frequencies will
>be attenuated by the air in the path from source to ear.  Also, the microphone
>used to get the acoustic signal into the Fourier analyzer has a non-flat
>frequency response.

Any respectable lab setup will use a calibrated mic, and correct for
that in the measurements.

Of course, even ignoring all the other effects, there's the very real
effect that the body (and head, for that matter) have on the
percieved signal, as well as relative position and orientation of
speaker and listener, all of which effect the spectrum of the signal
in the ear.
-- 
Jonathan E. Quist                              INTERACTIVE Systems Corporation
jeq@i88.isc.com  '71 CL450-K4 "Gleep", DoD #094        Naperville, IL
        There are many things a person should experience in a lifetime.
       Among them are an infant's first cry, and an infant's first laugh.

He probably meant that the sound from mouth is in kind of complicated pattern
since it is just from a block source, the sound near ear is the sound far from
its source, which will be treated as a parallel uniformed sound. i.e. in uniformpattern. Usually the wave equations will be different when you deal with the
sound near source and the sound in universe.


Once being an Acoustician

In article <1992Nov17.210853.14838@i88.isc.com> jeq@i88.isc.com (Jonathan E. Quist) writes:
>In article <Nov17.153055.54833@yuma.ACNS.ColoState.EDU> gw214790@LANCE.ColoState.Edu (Galen Watts) writes:
>>In article <1992Nov17.012614.20277@athena.mit.edu> philo@athena.mit.edu (philo) writes:
>>>lecturer once. One of the things that he said was that a spectrum analysis of the
>>>speach right near the ear of the listener did not agree with the spectrum of the
>>>sound as it left the mouth of the person who is talking. However, the fourrier
>>>components agreed to a large degree.
>>>
>>>Does any one have a better understanding of this concept that I do? I think
>>>this could be a very interesting question.
>>>-philo.
>>>dakhlak.... hawn nazl s suruur?
>>>				(Ziad)
>>
>>
>>Unless you were in an anechoic chamber, the reverberent field will always
>>change the frequency content of any acoustic signal.  High frequencies will
>>be attenuated by the air in the path from source to ear.  Also, the microphone
>>used to get the acoustic signal into the Fourier analyzer has a non-flat
>>frequency response.
>
>Any respectable lab setup will use a calibrated mic, and correct for
>that in the measurements.
>
>Of course, even ignoring all the other effects, there's the very real
>effect that the body (and head, for that matter) have on the
>percieved signal, as well as relative position and orientation of
>speaker and listener, all of which effect the spectrum of the signal
>in the ear.
>-- 
>Jonathan E. Quist                              INTERACTIVE Systems Corporation
>jeq@i88.isc.com  '71 CL450-K4 "Gleep", DoD #094        Naperville, IL
>        There are many things a person should experience in a lifetime.
>       Among them are an infant's first cry, and an infant's first laugh.


With MLSSA or TEF or even spectrum analyzers like ARIEL's the energy
reaching the measurment device can factor out the response of the
microphone knowing it's measurments. These devices can also sort out the
direct sound and reflections from the room or any surface reflector.

In response to the original post, I think what was being talked about is
the spectrum content of a voice is different on-axis coming out of the
mouth from off-axis such as by the ear. Anyone that has listened to
themselves over tape recorders such as Video or Phone anwsering machines
knows that we sound different to ourselves live than from these recordings
for many reason's acoustical and mechanical transmission through the body.

Dave Wright