FFT length and sampling frequency relationship

Hi All,

        i was going through DSP book by proakis, there i came across
the following realted to for which sampling frequency what is the fft
lenght to be used like,

      Sampling Freq       FFT Length
       8KHz                        256
       22KHz                      512
       32KHz                      1024
       44.1/48KHz               2048

     My query is on what basic the fft length is calculated related to
the sampling frequency??????  but my understanding is it only depends
upon the frequency resolution required.

   looking for the reply,

    with regards,
    Prasad

mailprassi@gmail.com skrev:
> Hi All,
>
>         i was going through DSP book by proakis, there i came across
> the following realted to for which sampling frequency what is the fft
> lenght to be used like,
>
>       Sampling Freq       FFT Length
>        8KHz                        256
>        22KHz                      512
>        32KHz                      1024
>        44.1/48KHz               2048
>
>      My query is on what basic the fft length is calculated related to
> the sampling frequency??????  but my understanding is it only depends
> upon the frequency resolution required.

This has to depend on the application. A table like this doesn't make
sense unless there are some established rules for what is "sufficient
quality" of some sort.

Is this table given in a context that might make sense? Form some
of the sampling rates, I'd guess the application could be some sort
of audio or speech processing?

Rune

Hi Prasad,

it could help to explain the table to you if you would specify the
book's edition number and the page where you found the table, table
number or section number, something like this. On first look, it
doesn't make sense to me without other definitions connected to the
values.

stereo



mailprassi@gmail.com wrote:
> Hi All,
>
>         i was going through DSP book by proakis, there i came across
> the following realted to for which sampling frequency what is the fft
> lenght to be used like,
>
>       Sampling Freq       FFT Length
>        8KHz                        256
>        22KHz                      512
>        32KHz                      1024
>        44.1/48KHz               2048
>
>      My query is on what basic the fft length is calculated related to
> the sampling frequency??????  but my understanding is it only depends
> upon the frequency resolution required.
> 
>    looking for the reply,
> 
>     with regards,
>     Prasad

mailprassi@gmail.com wrote:
> Hi All,
> 
>         i was going through DSP book by proakis, there i came across
> the following realted to for which sampling frequency what is the fft
> lenght to be used like,
> 
>       Sampling Freq       FFT Length
>        8KHz                        256
>        22KHz                      512
>        32KHz                      1024
>        44.1/48KHz               2048
> 
>      My query is on what basic the fft length is calculated related to
> the sampling frequency??????  but my understanding is it only depends
> upon the frequency resolution required.

Note that the duration of the analyzed signal is about as constant as 
powers of two can accomplish. In other words, the bin spacing in Hz 
varies little from one case to the next. Perhaps that property is 
relevant for the application.

Jerry
-- 
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