Fw: Odd behaviur of "Fractional Interpolator"

Uhm, so it’s a little bit confusing.
Another strange problem is that if i put a 0.64 value of interpolation,
and my flow graph is a file souce->fractional interpolator->file sink,
and my source file is 1GB of data, i’m expecting a 1GB*1/0.64 output
filesize. But when i run the graph i get a 800MB of output filesize,
minor than the source file. I cannot undestand this…
Thank you.

From: Marcus D. Leech
Sent: Tuesday, October 18, 2011 7:45 PM
To: [email protected]
Subject: Re: [Discuss-gnuradio] Odd behaviur of “Fractional
Interpolator”

On 18/10/11 01:38 PM, Mattia R. wrote:
I’m using gnuradio-3.3.0 with GRC.
I’ve builded a graph with a Complex cosine (8Ms/s of sample rate and 1
MHz of frequency), the fractional interpolator with 12/8 value for
interpolation and a FFT sink with 12MS/s of sample rate. (throttle block
included).
I’m expecting to see a 1MHz cosine with the FFT, but i see a 2.25MHz
cosine. If i put 8/12 (the inverse) i see the (correct) 1MHz cosine.
Why?
If i use the Rational resampler, with interpolation 12 and decimation
8, i see the correct 1MHz cosine. What’s wrong with fractional
interpolator block?


Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Because the fractional interpolator takes the inverse as the desired
fraction–think of it as a decimation
ratio.


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

Sorry, the filesize is my mistake. All okay now. Thank you.

From: Mattia R.
Sent: Tuesday, October 18, 2011 8:12 PM
To: gnu radio
Subject: Fw: [Discuss-gnuradio] Odd behaviur of “Fractional
Interpolator”

Uhm, so it’s a little bit confusing.
Another strange problem is that if i put a 0.64 value of interpolation,
and my flow graph is a file souce->fractional interpolator->file sink,
and my source file is 1GB of data, i’m expecting a 1GB*1/0.64 output
filesize. But when i run the graph i get a 800MB of output filesize,
minor than the source file. I cannot undestand this…
Thank you.

From: Marcus D. Leech
Sent: Tuesday, October 18, 2011 7:45 PM
To: [email protected]
Subject: Re: [Discuss-gnuradio] Odd behaviur of “Fractional
Interpolator”

On 18/10/11 01:38 PM, Mattia R. wrote:
I’m using gnuradio-3.3.0 with GRC.
I’ve builded a graph with a Complex cosine (8Ms/s of sample rate and 1
MHz of frequency), the fractional interpolator with 12/8 value for
interpolation and a FFT sink with 12MS/s of sample rate. (throttle block
included).
I’m expecting to see a 1MHz cosine with the FFT, but i see a 2.25MHz
cosine. If i put 8/12 (the inverse) i see the (correct) 1MHz cosine.
Why?
If i use the Rational resampler, with interpolation 12 and decimation
8, i see the correct 1MHz cosine. What’s wrong with fractional
interpolator block?


Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Because the fractional interpolator takes the inverse as the desired
fraction–think of it as a decimation
ratio.


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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