RE: [Discuss-gnuradio] Output of usrp_rx_cfile and Input of ATSC demodulator

[Wuest Brandon-WTVR47]

When you specify a bit width of 8, does that not pack them in to a
single byte rather than an integer?  If I am correct in this, then I am
effectively cutting my data rate by 4, which is a huge boost.  Though I
will loose some value due to quantization noise, the point is to cut
down the chance of an under run, while maintaining the correct format
for the ATSC demodulator.

Just as if you use the flag -s, you get 16-bit values contained within a
short (2 bytes), not an entire word.

-----Original Message-----
From: John Clark [mailto:address@hidden 
Sent: Thursday, November 29, 2007 1:27 PM
To: Wuest Brandon-WTVR47
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Output of usrp_rx_cfile and Input of
ATSC demodulator

Wuest Brandon-WTVR47 schrieb:
> All,
>  
> In the hopes of trying to understand the various aspects of GNU Radio 
> and the USRP hardware, I am trying to use the ATSC demodulator 
> included with GNU Radio to create an MPEG transport stream from the 
> output of usrp_rx_cfile.py.  Something I know has been discussed many 
> times on this forum.
>  
> I am having a problems with disk writing not being able to keep up 
> with the high data rate, so I am trying to do a little manipulation of

> the IQ data to get around this.  What I am trying to do it get 8-bit 
> samples from the usrp (which my disk can keep up with) and then before

> I feed that in to interp.py, I convert every pair of bytes to a 
> complex<float>.

Perhaps I missed something here... if you are having problems recording
2 '8-bit' integers, why would converting those integers to floats, that
is creating now 2 4 byte quantities... improve performance in any way.

Back when I worried about such things, I usually thought about
maintaining everything in 'integer' form, and should I have needed a
'FFT', I would start thinking about Galois Fields, prime generator
polynomials... and the like, but stay with integers...

John Clark.