Re: [Discuss-gnuradio] Format of captured data

[Josh Blum]

> Apologies for the wrong information. I don't mean to side track the
> original query, but I have a couple of questions.
>
> I found this in the FAQ.
>
> "Regarding the bandwidth, we can sustain 32MB/sec across the USB. All
> samples sent over the USB interface are in 16-bit signed integers in
> IQ format, i.e. 16-bit I and 16-bit Q data (complex) which means 4
> bytes per complex sample. This resulting in a (32MByte per sec/4Byte)
> 8Mega complex samples/sec across the USB."
>
> So I guess here we are assuming that we are using usrp_s() ?

Everything is 16 bits. usrp_c just casts the interleaved shorts into 
floats, whereas usrp_s leaves the interleaved shorts as they are. That 
is why the min and max values are +/- 2**15 even in floating point.

>  Also, since the ADC only has 12bit precision, are the extra bits used
> to retain precision as we go through the CIC and Halfband filters?

Also, being byte-aligned is a key issue here. Imagine what would happen 
if the host had to shift every sample in memory.

> If I were to use the std_4rx_0tx.rbf and usrp_s() to receive 4
> channels. Then am I correct in saying that I need to have a
> deinterleaver with 8 channels after the usrp_s() from which I will
> club channel 0 and 1 into a new complex stream (similarly for channel
> 2 and 3 etc) to get 4 complex streams?

does the usrp_s/c answer clear this up for you?

-Josh