Re: [Discuss-gnuradio] Format of captured data

[Karthik]

On Thu, May 28, 2009 at 12:42 AM, Josh Blum <address@hidden> wrote:
>
>> 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
>

Thanks Josh,

That clears things up for me.

Regards,
Karthik