Re: [Discuss-gnuradio] lack of understanding the different formats to store samples

[Nikos Balkanas]

IQ files are binary files with the raw stream and no headers. Depending on sample resolution, these are complex pairs of either floats or bytes.

Conversion of bytes to floats is given by the code:

float f;

byte b;

f = (b - 127)/128;

HTH

Nikos

On Wed, Mar 16, 2016 at 4:04 PM, Henry Barton <address@hidden> wrote:

This sounds interesting; I too have been wondering how IQ files worked. I thought it must be alternating I bytes and Q bytes, or with >8-bit radios, I words and Q words. But maybe the packed byte system is right, since I can feed IQ recordings in WAV format directly into GNUradio without stripping the headers.

> To: address@hidden; address@hidden
> From: address@hidden
> Date: Wed, 16 Mar 2016 10:24:02 +0100
> Subject: Re: [Discuss-gnuradio] lack of understanding the different formats to store samples
>
> Ok, let "I" and "Q" be single bits each, so each byte would then be
>
> IQIQIQIQ
>
> if I had to take a guess.
>
> You can get get back something that GR commonly deals with by doing
>
> packed to unpacked (type=B, bits per chunk = 1, endianness=your machine)
> -> IChar to Complex
>
> Best regards,
> Marcus
> On 16.03.2016 08:13, Ralph A. Schmid, dk5ras wrote:
> > Each byte seems to contain 4 1 bit I/Q samples. This is the text from the
> > readme:
> >
> > "The output file size can be reduced by using "-b 1" option to store four
> > 1-bit I/Q samples into a single byte."
> >
> > Ralph.
> >
> >> -----Original Message-----
> >> From: discuss-gnuradio-bounces+ralph=address@hidden
> >> [mailto:discuss-gnuradio-bounces+ralph=address@hidden] On Behalf Of
> >> Marcus Müller
> >> Sent: Friday, March 11, 2016 2:53 PM
> >> To: address@hidden
> >> Subject: Re: [Discuss-gnuradio] lack of understanding the different
> > formats
> >> to store samples
> >>
> >> In what format are your 1bit samples? I'd assume they are just the fact
> >> whether a byte is 0x00 or 0x01; in that case, just use unpacked to packed.
> >>
> >> On 03/11/2016 10:24 AM, Ralph A. Schmid, dk5ras wrote:
> >>> Hi,
> >>>
> >>> Being an RF guy I must admit that I am somehow lost in the different
> >>> ways how samples are stored in files. I stumbled over this question
> >>> when I experimented with https://github.com/osqzss/gps-sdr-sim. It
> >>> works great when using 16 bit samples and using a simple two-block grc
> >>> file, feeding them directly from a file source to the UHD sink.
> >>> However the 1 bit variant sounds promising, as the files are much
> >>> smaller this way and also the generation of them runs much faster.
> >>>
> >>> It must only be a matter of finding the right blocks and the right
> >>> settings to convert this, but my google search was highly confusing,
> >>> most probably due to different names for the same thing.
> >>>
> >>> So I do not only ask for how to use "four 1-bit I/Q samples into a
> >>> single byte" (taken from the readme of the gps-sdr-sim), but for a
> >>> more general overview how this stuff is done, to be prepared for other
> >>> upcoming questions of this kind :) Up to now I solved those issues by
> >>> an educated guess or even by try and error, what is not very
> > satisfying...
> >>> Ralph.
> >>>
> >>>
> >>> _______________________________________________
> >>> Discuss-gnuradio mailing list
> >>> address@hidden
> >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >>
> >> _______________________________________________
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