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Forum index » Science and Technology » Physics » Acoustics
frequency resolution of an acoustic signal
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jrenfree@gmail.com
science forum beginner


Joined: 10 Jul 2006
Posts: 1

PostPosted: Mon Jul 10, 2006 7:02 pm    Post subject: frequency resolution of an acoustic signal Reply with quote

I ran an experiment which involved sending a 2ms broad bandwidth signal
and recording the reflected signal, but I'm curious as to what the
frequency resolution is. The signal has a bandwidth of 18kHz, with a
center frequency of 18kHz and a start and stop frequency of 9kHz and
27kHz, respectively.

I'm a little confused as to what would be limiting the frequency
resolution though. I've heard of this time-bandwidth product, although
I'm not sure how to interpret it. Would it be this that is limiting
the resolution or is it the sampling frequency of the function
generator that I'm using?

Thanks,
-Josiah
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TheGhost
science forum addict


Joined: 09 Aug 2005
Posts: 85

PostPosted: Tue Jul 11, 2006 12:14 am    Post subject: Re: frequency resolution of an acoustic signal Reply with quote

jrenfree@gmail.com wrote in
news:1152558137.466352.182990@b28g2000cwb.googlegroups.com:

Quote:
I ran an experiment which involved sending a 2ms broad bandwidth signal
and recording the reflected signal, but I'm curious as to what the
frequency resolution is. The signal has a bandwidth of 18kHz, with a
center frequency of 18kHz and a start and stop frequency of 9kHz and
27kHz, respectively.

I'm a little confused as to what would be limiting the frequency
resolution though. I've heard of this time-bandwidth product, although
I'm not sure how to interpret it. Would it be this that is limiting
the resolution or is it the sampling frequency of the function
generator that I'm using?

Thanks,
-Josiah


Frequency resolution is established by the duration of your signal. The
bandwidth of your signal dosen't matter. If your signal is 2msec in
duration, you will not be able to resolve (identify) spectral components in
your signal that are separated in frequency by less than 1/(0.002)sec or
500Hz. This is the standard definition of frequency resolution. If you
mean something different, you need to clarify what you mean by frequency
resolution.

Another way of looking at frequency resolution is to consider how long you
have to look at a multi-frequency signal to establish that there are two
components separated by 100Hz (eg 10.0KHz + 10.1KHz). The answer is
100mSec.
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TheGhost
science forum addict


Joined: 09 Aug 2005
Posts: 85

PostPosted: Tue Jul 11, 2006 12:22 am    Post subject: Correction: Re: frequency resolution of an acoustic signal Reply with quote

The Ghost <theghost@hotmail.com> wrote in
news:T3Csg.32046$RW2.27896@fe05.news.easynews.com:

Quote:
jrenfree@gmail.com wrote in
news:1152558137.466352.182990@b28g2000cwb.googlegroups.com:

I ran an experiment which involved sending a 2ms broad bandwidth
signal and recording the reflected signal, but I'm curious as to what
the frequency resolution is. The signal has a bandwidth of 18kHz,
with a center frequency of 18kHz and a start and stop frequency of
9kHz and 27kHz, respectively.

I'm a little confused as to what would be limiting the frequency
resolution though. I've heard of this time-bandwidth product,
although I'm not sure how to interpret it. Would it be this that is
limiting the resolution or is it the sampling frequency of the
function generator that I'm using?

Thanks,
-Josiah


Frequency resolution is established by the duration of your signal.
The bandwidth of your signal dosen't matter. If your signal is 2msec
in duration, you will not be able to resolve (identify) spectral
components in your signal that are separated in frequency by less than
1/(0.002)sec or 500Hz. This is the standard definition of frequency
resolution. If you mean something different, you need to clarify what
you mean by frequency resolution.

Another way of looking at frequency resolution is to consider how long
you have to look at a multi-frequency signal to establish that there
are two components separated by 100Hz (eg 10.0KHz + 10.1KHz). The
answer is 100mSec.


The answer is 10mSec (1/100Hz).
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jerry1114
science forum beginner


Joined: 20 Jul 2006
Posts: 1

PostPosted: Thu Jul 20, 2006 1:14 am    Post subject: Re: frequency resolution of an acoustic signal Reply with quote

HI,
The frequency resolution is determined by the length of the signal
pulse you send out. If you have a 2msec pulse going out then you don't
have more than 2 msec of data to analyze. Look at doing an FFT or
whatever with this signal of duration 2 ms and you'll see that the
resolution is independent of the center, start and stop frequencies for
the most part. You'll get the most bandwidth out of a square pulse of
2 ms duration, but that shouldn't be your only consideration.

Regards,
Jerry
jrenfree@gmail.com wrote:
Quote:
I ran an experiment which involved sending a 2ms broad bandwidth signal
and recording the reflected signal, but I'm curious as to what the
frequency resolution is. The signal has a bandwidth of 18kHz, with a
center frequency of 18kHz and a start and stop frequency of 9kHz and
27kHz, respectively.

I'm a little confused as to what would be limiting the frequency
resolution though. I've heard of this time-bandwidth product, although
I'm not sure how to interpret it. Would it be this that is limiting
the resolution or is it the sampling frequency of the function
generator that I'm using?

Thanks,
-Josiah
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