CaptainBassline
Posts: 11
Joined: Thu Nov 15, 2012 9:49 am

Full duplex yet??

Sat Mar 16, 2013 11:18 am

Hi all...

From the outset I've been having trouble achieving simultaneous audio input & output from the Pi through an external soundcard, using PDext. This was some time ago, and I have been wondering if anyone knows this to have been resolved yet? I've trawled through lots of posts on this board and found no answer, but just thought I'd ask anyway :)

Thanks

Spid
Posts: 525
Joined: Sat Jan 19, 2013 12:47 pm

Re: Full duplex yet??

Sat Mar 16, 2013 12:13 pm

I was under the impression that USB Soundacards could only achieve half-duplex due to the limitations of the USB 2 Bus ?

I belive USB 3 will allow full-duplex !

"Comparing USB3.0 to USB2.0, the difference between the two are like Full-duplex and Half Duplex modes. USB3.0 can receive
and transfer data at the same time while USB2.0 can only either transfer or receive data. It may not mean much for mobile
storage but it does however provide multi-thread capability, making USB3.0 more suited for mass multimedia data transfer use!"


Maybe Bluetooth ???? http://en.wikipedia.org/wiki/Bluetooth_ ... 28L2CAP.29

Logical link control and adaptation protocol (L2CAP)
L2CAP is used within the Bluetooth protocol stack. It passes packets to either the Host Controller Interface (HCI) or on a hostless
system, directly to the Link Manager/ACL link.
L2CAP's functions include:
Multiplexing data between different higher layer protocols..............................
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I will always assume you are running Raspbian for desktop and Raspbmc for XMBC !

CaptainBassline
Posts: 11
Joined: Thu Nov 15, 2012 9:49 am

Re: Full duplex yet??

Sat Mar 16, 2013 12:30 pm

My card is definitely USB 2.0, and it has fine duplex on my lappy under Ubuntu... It must rapidly (seemlessly?) switch between in/out to achieve this. I guess this is where the Pi has been failing? I believe Miller P. Has been musing over this for some time, I'm hoping he has found a fix!

User avatar
AutoStatic
Posts: 326
Joined: Tue Jan 01, 2013 10:27 pm
Contact: Website

Re: Full duplex yet??

Sat Mar 16, 2013 1:17 pm

http://wiki.linuxaudio.org/wiki/raspberrypi

So simultaneous audio input and output is perfectly possible. Not sure about USB2 interfaces though, what kind of interface do you have? And yes, USB1.1 and USB2.0 are half-duplex but that doesn't mean you can't have simultaneous audio input and output, the intervals between data going in and out is really small (if I'm correct it's 1ms).
RPi and real-time, low-latency audio: http://wiki.linuxaudio.org/wiki/raspberrypi
RPi audio repository: http://rpi.autostatic.com/
RPi and audio blog: https://autostatic.com/tag/raspberrypi/

Spid
Posts: 525
Joined: Sat Jan 19, 2013 12:47 pm

Re: Full duplex yet??

Sat Mar 16, 2013 3:56 pm

AutoStatic wrote:http://wiki.linuxaudio.org/wiki/raspberrypi

So simultaneous audio input and output is perfectly possible. Not sure about USB2 interfaces though, what kind of interface do you have? And yes, USB1.1 and USB2.0 are half-duplex but that doesn't mean you can't have simultaneous audio input and output, the intervals between data going in and out is really small (if I'm correct it's 1ms).
So USB 1/2 is half-duplex and would need USB3 for full-duplex which is the answer to the OP question

Maybe a lightweight Linux Distro like piCore or Slitaz would overcome any resource deficiencies the OP is experienceing ?
I will always assume you are running Raspbian for desktop and Raspbmc for XMBC !

User avatar
AutoStatic
Posts: 326
Joined: Tue Jan 01, 2013 10:27 pm
Contact: Website

Re: Full duplex yet??

Sat Mar 16, 2013 4:52 pm

Spid wrote:So USB 1/2 is half-duplex and would need USB3 for full-duplex which is the answer to the OP question.
It's the answer to the OP question in the subject but not the answer to the OP question in the post itself. I get the idea that the OP is mixing up simultaneous audio in and out with full-duplex.
Spid wrote:Maybe a lightweight Linux Distro like piCore or Slitaz would overcome any resource deficiencies the OP is experienceing ?
I can achieve latencies below <10ms with duplex audio on Raspbian. So I guess resource deficiencies are not the issue here.
RPi and real-time, low-latency audio: http://wiki.linuxaudio.org/wiki/raspberrypi
RPi audio repository: http://rpi.autostatic.com/
RPi and audio blog: https://autostatic.com/tag/raspberrypi/

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