# Complex bandpass vs real low-pass

**URL:** <https://www.ruby-forum.com/t/complex-bandpass-vs-real-low-pass/219435>\
**Category:** GNU Radio\
**Created:** [May 2, 2012, 11:56pm UTC](https://www.ruby-forum.com/t/complex-bandpass-vs-real-low-pass/219435 "2012-05-02T23:56:22Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\
**Post date:** [May 2, 2012, 11:56pm UTC](https://www.ruby-forum.com/t/complex-bandpass-vs-real-low-pass/219435/1 "2012-05-02T23:56:22Z")

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I have been in the habit of using complex-bandpass filters even when I’m  
just looking for a symmetric response. I did some measurements  
today and found a 40-45% performance advantage to using a low-pass  
real filter when a symmetric response is desired. What’s the “crux”  
of the performance difference?

Needless to say, I ran around and changed all my recent “stuff” to use  
low-pass filters 🙂

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

> **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)**
>
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**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [May 3, 2012, 12:00am UTC](https://www.ruby-forum.com/t/complex-bandpass-vs-real-low-pass/219435/2 "2012-05-03T00:00:06Z")

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On Wed, May 2, 2012 at 2:55 PM, Marcus D. Leech [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> I have been in the habit of using complex-bandpass filters even when I’m  
> just looking for a symmetric response. I did some measurements  
> today and found a 40-45% performance advantage to using a low-pass real  
> filter when a symmetric response is desired. What’s the “crux”  
> of the performance difference?
> 
> Needless to say, I ran around and changed all my recent “stuff” to use  
> low-pass filters 🙂

Complex \* complex multiplies are more computationally expensive than  
complex \* real. For edification and titillation you can read the  
volk\_32fc\_x2\_multiply\_32fc source. There’s an Orc version too which is  
easier to read. The moral of the story is you should probably avoid  
complex  
coefficients unless you know you need them.

–n

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**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [May 3, 2012, 12:08am UTC](https://www.ruby-forum.com/t/complex-bandpass-vs-real-low-pass/219435/3 "2012-05-03T00:08:45Z")

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On 05/02/2012 05:59 PM, Nick F. wrote:

> Complex \* complex multiplies are more computationally expensive than  
> complex \* real. For edification and titillation you can read the  
> volk\_32fc\_x2\_multiply\_32fc source. There’s an Orc version too which is  
> easier to read. The moral of the story is you should probably avoid  
> complex coefficients unless you know you need them.
> 
> –n

Oooh, titillation. Sign me up 🙂

Yup, that makes sense.

–  
Marcus L.  
Principal Investigator  
Shirleys Bay Radio Astronomy Consortium

> **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)**
>
> Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami.