Re: packetized audio transmission using GMSK modulation

[Marcus Müller]

Hi Amir,

you're right, the packet encoder and decoder have *long* been 
deprecated, because they sometimes simply drop data. Don't use them at all.

Also, you're using GNU Radio 3.7. Don't use that to design new software, 
it's really in "legacy maintenance". The current stable release series 
is 3.8.x.x.

Also, at least in your loopback.grc, you should NEVER use throttle in 
the same flowgraph as a hardware sink (i.e. the audio sink). GRC should 
print a warning about that, unless it's *really* old.

Are you sure your audio file contains audio sampled at the same rate 
that you let your audio sink sample?


Best regards,

Marcus

On 8/10/20 2:53 AM, Amir Hossein Aalipour wrote:
> Hi all
> As a newbie at gnuradio, currently I have two problems. I want to 
> transmit an audio file with gmsk modulation. I used the below 
> transmitter and receiver flow graphs which include packet 
> encoder/decoder blocks. It works but the audio I hear is "like" that 
> it is playing 10x faster than normal that it gets intermittent too 
> much and sound card can't follow it! I couldn't find why. Can you 
> please tell me what i have missed here?
>
> Can the packet encoder/decoder be the cause?
>
> I guessed maybe the packet encoder/decoder are the sources of problem 
> (because seemingly they are obsolete). Therefore I tried to implement 
> what these two blocks do. I reached at the loopback configuration 
> below in which I packed the data going into modulator. But it does not 
> work. no warning no error but nothing to hear either! then I removed 
> the mod/demod combination and put a tag gate block. This time it was 
> ok as expected of course. This shows something is wrong with the 
> mod/demod. I couldn't figure it out and this is now my second problem. 
> Please guide me to the right way.
>
> The format object I used is: 
> digital.header_format_default(digital.packet_utils.default_access_code, 0)
> and the endianness of repack bits block is MSB with length tag key of 
> packet_len.
>
> I'm using Ettus B205 SDR boards on Ubuntu 18.04 and GRC 3.7.13.4.
>
> Thank you in advance.
>
>
> --
> Amir Hossein Aalipour
> MSc student of Electronics engineering
> Department of Electrical Engineering
> Sharif University of Technology