AVB Audio Endpoint Kit/XMOS AVB - Max Channels/Listeners?

Technical discussions related to any XMOS development kit or reference design. Eg XK-1A, sliceKIT, etc.
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Chendy
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AVB Audio Endpoint Kit/XMOS AVB - Max Channels/Listeners?

Post by Chendy »

1. Number of 'listerners'

What is the maximum amount devices that you can practically have on one AVB network? (using the L2 AVB reference design kit)

Is number of devices just limited by the 100 MBit/s bandwidth, and so a function of the number of audio channels and audio bid depth? Or are there any other limitations?

What sort of number of listeners could I expect to practically get using the L2 based kit (24-bit @ 48kHz), where each listener receives a unique stereo channel?

2. Computer based 'talker'

Are there any examples of using a PC as the source of the AVB audio stream; using a PC as the talker? If no examples are freely available, what would need to be done in order stream multichannel audio via a C++ application to multiple listeners?

Although a clever multichannel audio driver that registers the audio outputs with a operating system would be ideal, a method using bare Ethernet would suffice (e.g. C++ with a Ethernet library).

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This was sort of answered here:
https://www.xcore.com/forum/viewtopic.php?f=7&t=118

Where it was suggested that 16 channels 24-bit 48 kHz would be do-able and would take 30 Mbit/s of bandwidth: What about 48 channel 24-bit 48 kHz? or 48 channel 16-bit 48 kHz?

Thanks

Chendy


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Andy
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Post by Andy »

Hi Chendy,

For typical bandwidth usage see page 70 of the XMOS AVB design guide: https://www.xmos.com/download/public/AV ... 1.0%29.pdf

The standards allow a maximum of 75% of link bandwidth to be used for AVB streams. This will limit AVB bandwidth on a 100Mbit link to less than 75Mbit/s. 32 channels in a single stream @ 24bit/48KHz should be OK. I haven't done the maths but 48 channels might not be possible. If it's just over the limit, it may still be possible by using a different audio format than IEC 61883-6, with less overhead. One such format is being proposed as part of an upcoming amendment to 1722.

Are you planning to have multiple L2 based AVB Listeners that pull stereo channels from a single high channel count stream?

Regarding the computer based Talker: AVB requires new Ethernet hardware to do accurate time stamping of packets. The latest Apple Macs are shipping with such hardware and I believe OS X Lion has an AVB stack + 1722.1 control.

There's no AVB support on Windows/Linux but with the correct NIC and Layer 2 Ethernet access, an AVB stack could be developed.
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Chendy
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Post by Chendy »

Hi Andy,

Thanks for the detailed and informative response.
Are you planning to have multiple L2 based AVB Listeners that pull stereo channels from a single high channel count stream?
Yes exactly.
Regarding the computer based Talker: AVB requires new Ethernet hardware to do accurate time stamping of packets. The latest Apple Macs are shipping with such hardware...
Crap! you need a Mac. This all looks very involved anyway. I may wait until AVB is more mature and there is more documentation/experience etc - I am a mere noob

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Alois
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Post by Alois »

Andy wrote: Regarding the computer based Talker: AVB requires new Ethernet hardware to do accurate time stamping of packets. The latest Apple Macs are shipping with such hardware and I believe OS X Lion has an AVB stack + 1722.1 control.

There's no AVB support on Windows/Linux but with the correct NIC and Layer 2 Ethernet access, an AVB stack could be developed.
Hi Andy - with respect to needing new Ethernet hardware, it this true for a computer functioning as a listener vs. a talker as well?

FWIW, I recall that Audinate's Dante products are AVB-compliant and provide the ability to load a device driver on a computer (Win) that allows it to be a listener on the AVB-network. Not sure if that's part of their proprietary additions to AVB but was curious to know if the distinction between listening / talking made a difference.

Are you aware of any major OEM Ethernet NIC vendors that supply the necessary timing on their latest products?

Thanks, Al
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Andy
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Post by Andy »

Alois wrote:Hi Andy - with respect to needing new Ethernet hardware, it this true for a computer functioning as a listener vs. a talker as well?

FWIW, I recall that Audinate's Dante products are AVB-compliant and provide the ability to load a device driver on a computer (Win) that allows it to be a listener on the AVB-network. Not sure if that's part of their proprietary additions to AVB but was curious to know if the distinction between listening / talking made a difference.

Are you aware of any major OEM Ethernet NIC vendors that supply the necessary timing on their latest products?

Thanks, Al
Yes - both the talker and listener should have the proper gptp timestamping hardware. I suppose it's possible to have an 'out of spec' listener that ignores the presentation time and doesn't properly sync with other listeners.

I'm not familiar with Audinate's Dante products. Do they use standard Ethernet NICs? If they do they I doubt it's a fully in-spec AVB listener.

I'm not aware of any such 'plug in' Ethernet NICs at the moment but it's only a matter of time before they appear, as Broadcom's latest Ethernet silicon is AVB compliant (and already shipping in Apple Macs).
crappidy
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Post by crappidy »

Hey,

see https://abc.statusbar.com/

Maximal 45 channels per stream @ 48kHz/24bit are possible in an AVB network.
More than 45 channels would exceed the 75% bandwith in an 100MBit network.
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