Re: [Discuss-gnuradio] Bandwidth Across USB

[Eric Blossom]

On Wed, Apr 05, 2006 at 02:30:30PM -0700, jjw wrote:
> 
> I know this is probably an extremely stupid question, but I wanted to get
> some verification.  I've noticed that the minimum decimation rate you can
> use in all of the sample programs is 4 (giving you an effective sampling
> rate of 16 MHz).  If you are transmitting 1 real channel of data (16 bits)
> at this rate,

Note that the standard FPGA build will not xfer a single real channel...

> that seems to be maxing out the USB transfer rate of 32 MB/s. 
> Am I correct in my deduction that you need to use a decimation rate of at
> least 8 in order to transmit complex data (such as for FM demodulation)
> successfully across the USB?  Thanks. 

Yes, decim = 8 gives 64e6/8 = 8MS/s complex.

In general, you want to use the highest decimation factor that works
for your application.  This offloads more of the crunching onto the
FPGA.

Eric