RE: dolby digital output

RE: dolby digital output

[James Courtier-Dutton]

> -----Original Message-----
> From: Hod McWuff [mailto:hod@wuff.dhs.org]
> Sent: 17 February 2002 18:21
> To: James Courtier-Dutton
> Subject: RE: [Alsa-devel] dolby digital output
>
>
>
> So, the upshot is that thanks to the AC3 latency spec, even with a
> lightning-fast encoder, it wouldn't work.
>
> >
> > I think it would be best for your application to do the mixing.
> >
>
> I think you may be right... but that still doesn't solve the additional
> latency, and digital output is still (unhappily) limited to two channels
> unless you're playing a canned stream, such as a dvd.
>
> Any other ideas on how to deal with that, or would an extension to
> S/PDIF be required?
>
I think some high speed S/PDIF is available which can do 8 Channel 96Khz 24
bit audio but very few PC sound cards can do that.

I would have preferred everything to be converted to packet technologies,
and then we could link all consumer equipment together with Ethernet cables!
Circuit based technologies are quite complicated because one has to worry
about clocking and synchronisation all the time.
With packet, each packet would just have a small header, with Stream ID,
duration of packet, Packet number, with maybe a timestamp if one needs to
synchronise two or more different streams together. Also circuit based
technologies have no error correction.

A simple 100 Megs Full duplex point to point Ethernet cable can handle just
about anything S/PDIF, USB, SCSI, IDE can throw at it.
Maybe that is why there is an IP version of SCSI now.

Cheers
James


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RE: dolby digital output

[Bob Ham]

On Sun, 2002-02-17 at 18:44, James Courtier-Dutton wrote:

> A simple 100 Megs Full duplex point to point Ethernet cable can handle just
> about anything S/PDIF, USB, SCSI, IDE can throw at it.

I assume you've seen http://magic.gibson.com/?

Bob

-- 
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RE: dolby digital output

[James Courtier-Dutton]

So all I need now, is an Digital Amp with an Ethernet port for all 6 Channel
PCM, AC3 and DTS output.
I already have an ethernet card for my PC and a HUB.

magic.gibson.com must be stupid not to realise that what we really want is
an AMP with an Ethernet port, not yet another sound card.

We could then just connect the AMP to the ethernet port on any PC, and have
perfect digital quality output.
Alsa would then not be needed, because once the audio is in packets, it
would be better to keep it that way in the application.

One could even use Radio Lan technologies, and thus remove all the cabling
as well.

Cheers
James


> -----Original Message-----
> From: alsa-devel-admin@lists.sourceforge.net
> [mailto:alsa-devel-admin@lists.sourceforge.net]On Behalf Of Bob Ham
> Sent: 18 February 2002 14:51
> To: James Courtier-Dutton
> Cc: alsa-devel@lists.sourceforge.net
> Subject: RE: [Alsa-devel] dolby digital output
>
>
> On Sun, 2002-02-17 at 18:44, James Courtier-Dutton wrote:
>
> > A simple 100 Megs Full duplex point to point Ethernet cable can
> handle just
> > about anything S/PDIF, USB, SCSI, IDE can throw at it.
>
> I assume you've seen http://magic.gibson.com/?
>
> Bob
>
> --
> Bob Ham: bob@ham.org
>
> My music: http://mp3.com/obelisk_uk
> GNU Hurd: http://hurd.gnu.org/
> Do your bit for UK drugs law reform: http://www.angeldeclaration.com/
>
> A pessimist expects the weather to get worse.
> An optimist hopes it will improve.
> A realist adjusts the sails.
>
>
> _______________________________________________
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> https://lists.sourceforge.net/lists/listinfo/alsa-devel


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RE: dolby digital output

[Bob Ham]

On Mon, 2002-02-18 at 15:46, James Courtier-Dutton wrote:

> magic.gibson.com must be stupid not to realise that what we really want is
> an AMP with an Ethernet port

Umm.. this *is* what magic can provide.  A guitar with a an ethernet
port, an amp with an ethernet port, a mixer with an ethernet port, a
computer with an ethernet port.. you name it.  (And when I say ethernet
here, I mean RJ45.)  Has the following specs:

32 channels @ 44.1 kHz x 32 bits
32 channels @ 48 kHz x 32 bits
16 channels @ 96 kHz x 32 bits
8 channels @ 192 kHz x 32 bits

This is over one cable; it's not a network in the sense of ethernet. 
You can't plug all your instruments into a 100baseTX hub, unfortunately,
but you can plug all your instruments into NICs in the back of your
computer.

-- 
Bob Ham: bob@ham.org

My music: http://mp3.com/obelisk_uk
GNU Hurd: http://hurd.gnu.org/
Do your bit for UK drugs law reform: http://www.angeldeclaration.com/

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An optimist hopes it will improve.
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RE: dolby digital output

[Bob Ham]

On Mon, 2002-02-18 at 16:26, Bob Ham wrote:
> Has the following specs:
> 
> 32 channels @ 44.1 kHz x 32 bits
> 32 channels @ 48 kHz x 32 bits
> 16 channels @ 96 kHz x 32 bits
> 8 channels @ 192 kHz x 32 bits

I should also note that this is full duplex.

-- 
Bob Ham: bob@ham.org

My music: http://mp3.com/obelisk_uk
GNU Hurd: http://hurd.gnu.org/
Do your bit for UK drugs law reform: http://www.angeldeclaration.com/

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An optimist hopes it will improve.
A realist adjusts the sails.


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Re: audio via ethernet (was: dolby digital output)

[stef]

I think sending realtime audio data via eternet will be
extremely difficult. It should be impossible to synchronize
sample clock via ethernet. So each device has to have its
own sample clock. This requires:

- resampling units (=no lossles connections possible)
or
- large buffers to slowly adapt sample rates
  (huge variing latency, clock jitter, ...)

With S/PDIF or any other common digital audio interface
it is at least possible to synchronize the receiver
to the transmitter's clock.
So you have to resample only if you're mixing
two or more digital inputs into one output.

If you're using pro equipment, it is even possible
to remotely clock digital audio sources (wordclock line).
In this case, you never have to resample and digital
audio processing can be lossless.

But with ethernet connections it is even impossible
to use separate digital-input amplifiers for
your right and left speaker. (unless you add
extra wordclock cabling...)

I don't know how the 'Wireless Multimedia Alliance'
(www.wimedia.org, JVC, Sony,...) is going to handle these
problems. Seems as if they extend the wireless lan standard
by some sort of real-time transfers. Like USB. They call
it IEEE 802.15.3.

Any comments? Am i wrong? What about Yamaha's MLAN (ieee1394)?

Stef(an).




James Courtier-Dutton wrote:
> 
> So all I need now, is an Digital Amp with an Ethernet port for all 6 Channel
> PCM, AC3 and DTS output.
> I already have an ethernet card for my PC and a HUB.
> 
> magic.gibson.com must be stupid not to realise that what we really want is
> an AMP with an Ethernet port, not yet another sound card.
> 
> We could then just connect the AMP to the ethernet port on any PC, and have
> perfect digital quality output.
> Alsa would then not be needed, because once the audio is in packets, it
> would be better to keep it that way in the application.
> 
> One could even use Radio Lan technologies, and thus remove all the cabling
> as well.
> 
> Cheers
> James

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RE: dolby digital output

[James Courtier-Dutton]

The magic web site did not mention anything about an AMP.


> -----Original Message-----
> From: alsa-devel-admin@lists.sourceforge.net
> [mailto:alsa-devel-admin@lists.sourceforge.net]On Behalf Of Bob Ham
> Sent: 18 February 2002 16:27
> To: James Courtier-Dutton
> Cc: ALSA Development Mailing List
> Subject: RE: [Alsa-devel] dolby digital output
> 
> 
> On Mon, 2002-02-18 at 15:46, James Courtier-Dutton wrote:
> 
> > magic.gibson.com must be stupid not to realise that what we 
> really want is
> > an AMP with an Ethernet port
> 
> Umm.. this *is* what magic can provide.  A guitar with a an ethernet
> port, an amp with an ethernet port, a mixer with an ethernet port, a
> computer with an ethernet port.. you name it.  (And when I say ethernet
> here, I mean RJ45.)  Has the following specs:
> 
> 32 channels @ 44.1 kHz x 32 bits
> 32 channels @ 48 kHz x 32 bits
> 16 channels @ 96 kHz x 32 bits
> 8 channels @ 192 kHz x 32 bits
> 
> This is over one cable; it's not a network in the sense of ethernet. 
> You can't plug all your instruments into a 100baseTX hub, unfortunately,
> but you can plug all your instruments into NICs in the back of your
> computer.
> 
> -- 
> Bob Ham: bob@ham.org
> 
> My music: http://mp3.com/obelisk_uk
> GNU Hurd: http://hurd.gnu.org/
> Do your bit for UK drugs law reform: http://www.angeldeclaration.com/
> 
> A pessimist expects the weather to get worse.
> An optimist hopes it will improve.
> A realist adjusts the sails.
> 
> 
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/alsa-devel

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RE: audio via ethernet (was: dolby digital output)

[James Courtier-Dutton]

When you switch from circuit based technologies to packet based ones, the
problems you have to solve are totally different.
1) Circuit requires clock sync across the entire network just like the old
TDM based telephone networks need. Packet does not.
2) Circuit introduces no delay for PCM data. Packet introduces a small
delay(normally less than 1 ms). (due to the size of the packet).
3) Circuit SPDIF cannot handle 8 channel 32bit audio. (The next DVD
standard). Packet technologies can.
4) All the problems of sending audio over packets have already been solved
by the Voice over IP people.
5) The only real problem left with packet is QOS (quality of service across
an entire network). But most people will just have point to point links in
an audio setup. E.g. From PC to AMP.

Cheers
James


> -----Original Message-----
> From: alsa-devel-admin@lists.sourceforge.net
> [mailto:alsa-devel-admin@lists.sourceforge.net]On Behalf Of stef
> Sent: 18 February 2002 17:01
> To: alsa-devel@lists.sourceforge.net
> Subject: Re: [Alsa-devel] audio via ethernet (was: dolby digital output)
>
>
> I think sending realtime audio data via eternet will be
> extremely difficult. It should be impossible to synchronize
> sample clock via ethernet. So each device has to have its
> own sample clock. This requires:
>
> - resampling units (=no lossles connections possible)
> or
> - large buffers to slowly adapt sample rates
>   (huge variing latency, clock jitter, ...)
>
> With S/PDIF or any other common digital audio interface
> it is at least possible to synchronize the receiver
> to the transmitter's clock.
> So you have to resample only if you're mixing
> two or more digital inputs into one output.
>
> If you're using pro equipment, it is even possible
> to remotely clock digital audio sources (wordclock line).
> In this case, you never have to resample and digital
> audio processing can be lossless.
>
> But with ethernet connections it is even impossible
> to use separate digital-input amplifiers for
> your right and left speaker. (unless you add
> extra wordclock cabling...)
>
> I don't know how the 'Wireless Multimedia Alliance'
> (www.wimedia.org, JVC, Sony,...) is going to handle these
> problems. Seems as if they extend the wireless lan standard
> by some sort of real-time transfers. Like USB. They call
> it IEEE 802.15.3.
>
> Any comments? Am i wrong? What about Yamaha's MLAN (ieee1394)?
>
> Stef(an).
>
>
>
>
> James Courtier-Dutton wrote:
> >
> > So all I need now, is an Digital Amp with an Ethernet port for
> all 6 Channel
> > PCM, AC3 and DTS output.
> > I already have an ethernet card for my PC and a HUB.
> >
> > magic.gibson.com must be stupid not to realise that what we
> really want is
> > an AMP with an Ethernet port, not yet another sound card.
> >
> > We could then just connect the AMP to the ethernet port on any
> PC, and have
> > perfect digital quality output.
> > Alsa would then not be needed, because once the audio is in packets, it
> > would be better to keep it that way in the application.
> >
> > One could even use Radio Lan technologies, and thus remove all
> the cabling
> > as well.
> >
> > Cheers
> > James
>
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/alsa-devel


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RE: dolby digital output

[Bob Ham]

On Mon, 2002-02-18 at 17:05, James Courtier-Dutton wrote:
> The magic web site did not mention anything about an AMP.

Magic is just a way to ferry audio data around.. that can be between any
audio devices.  The specification document gives a lot more details than
the site and has a few setup examples (including one with an amp :)

-- 
Bob Ham: bob@ham.org

My music: http://mp3.com/obelisk_uk
GNU Hurd: http://hurd.gnu.org/
Do your bit for UK drugs law reform: http://www.angeldeclaration.com/

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An optimist hopes it will improve.
A realist adjusts the sails.


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RE: audio via ethernet (was: dolby digital output)

[Jez Humble]

A parallel discussion has been taking place in the music bar
(music-bar@ampfea.org). I've given some of the more important comments
below.

>I think sending realtime audio data via eternet will be
>extremely difficult. It should be impossible to synchronize
>sample clock via ethernet. So each device has to have its
>own sample clock.

There is a protocol for determining which device is the master clock, which
is apparently "automatic and transparent to the user". Perhaps more urgent
are the fact that timing delays introduced by the fact that the Gibson
protocol DAISYCHAINS (which causes a whole host of other problems) will
screw MIDI up no end.

On the mLAN front, yes they do seem to be very similar, except that mLAN
works across FireWire, and is based on AMP (the Audio and Music Data
Transmission Protocol), which you can use without signing any agreements
with the evil guitar moloch from hell.

>4) All the problems of sending audio over packets have already been solved
>by the Voice over IP people.

I am somewhat sceptical: did they solve it for multiple streams of sound
sampled at 192khz? Indeed Gibson claims Magic provides up to 32 streams of
32-bit full-duplex sound at 192khz = 192Mbit/s, which is quite impressive
for ethernet, to say the least.

In fact the Gibson offering's main problems are with the control side of
things: Alastair Johnson pointed out the following quote from Gibson:

<evil guitar moloch>
Any device can assign a Control Link between a Source and a Target on the
network. The device making the assignment does not have to be the one with
either the Source or the Target. If that is the case, the assigning device
must issue the Assign Control Link message to both the Source and the
Target.
</evil guitar moloch>

<alastair>
I can already imagine the mayhem when two pieces of software/hardware try
and assign or remove Control Link to the same Sources and Targets. There
is no acknowledge message defined for this assign so if a control packet
is lost or if there are conflicting interests, there is no way to know.
Let alone fix it. (Hey why does the Cutoff knob on my Virus C suddenly
control the pitch of my Andromeda A& and my Kurzweill K2700?)
</alastair>

All in all the thing seems to be rather badly thought out.

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RE: dolby digital output

[Dan Hollis]

On 18 Feb 2002, Bob Ham wrote:
> On Sun, 2002-02-17 at 18:44, James Courtier-Dutton wrote:
> > A simple 100 Megs Full duplex point to point Ethernet cable can handle just
> > about anything S/PDIF, USB, SCSI, IDE can throw at it.
> I assume you've seen http://magic.gibson.com/?

sadly, magic is patent-encumbered.

-Dan
-- 
[-] Omae no subete no kichi wa ore no mono da. [-]


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RE: dolby digital output

[Dan Hollis]

On Mon, 18 Feb 2002, James Courtier-Dutton wrote:
> The magic web site did not mention anything about an AMP.

The specs do.

-Dan
-- 
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Re: audio via ethernet (was: dolby digital output)

[Dan Hollis]

On Mon, 18 Feb 2002, stef wrote:
> I think sending realtime audio data via eternet will be
> extremely difficult.

Why?

> It should be impossible to synchronize
> sample clock via ethernet.

Why?

Did you read the gibson magic spec?

-Dan
-- 
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Re: audio via ethernet (was: dolby digital output)

[stef]

Dan Hollis wrote:
> 
> On Mon, 18 Feb 2002, stef wrote:
> > I think sending realtime audio data via eternet will be
> > extremely difficult.
> 
> Why?
> 
> > It should be impossible to synchronize
> > sample clock via ethernet.
> 
> Why?
> 
> Did you read the gibson magic spec?

Oh, sorry! I thought you were talking about ethernet
(NICs, switches, hubs, MAC addressing, collisions)
and not just cat5 cables and a compatible physical layer.

Stef(an).

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Re: audio via ethernet (was: dolby digital output)

[Bob Ham]

On Mon, 2002-02-18 at 17:00, stef wrote:
> It should be impossible to synchronize
> sample clock via ethernet.

If it's possible for me to synchronise my PC clock to sub-millisecond
accuracy over *IP* on a LAN, I somehow doubt it'd be impossible to
synchronise word clocks over ethernet.

-- 
Bob Ham: bob@ham.org

My music: http://mp3.com/obelisk_uk
GNU Hurd: http://hurd.gnu.org/
Do your bit for UK drugs law reform: http://www.angeldeclaration.com/

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An optimist hopes it will improve.
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Re: audio via ethernet (was: dolby digital output)

[stef]

Bob Ham wrote:

> If it's possible for me to synchronise my PC clock to sub-millisecond
> accuracy over *IP* on a LAN, I somehow doubt it'd be impossible to
> synchronise word clocks over ethernet.

Sounds great! 20 nanoseconds would be enough.

But the problem in digital audio is that the clock has
to be readjusted in short intervals.

Anyway, which software/protocol/service do you use for
your clock synchronisation? _very_ interesting!

Thanks,

Stef(an).

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Re: audio via ethernet (was: dolby digital output)

[Dan Hollis]

On Tue, 19 Feb 2002, stef wrote:
> Anyway, which software/protocol/service do you use for
> your clock synchronisation? _very_ interesting!

Probably ntp. Works well, multicast mode should be excellent for this.

BTW if you use fixed size packets on fullduplex ethernet (as gibson's 
magic does), then sync should not be much of a problem. IIRC they also 
include synchronization data in the packets so that synchronization is 
easy.

-Dan
-- 
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Re: audio via ethernet (was: dolby digital output)

[Bob Ham]

On Mon, 2002-02-18 at 23:00, stef wrote:

> Anyway, which software/protocol/service do you use for
> your clock synchronisation? _very_ interesting!

The mother of all time protocols, NTP

http://www.eecis.udel.edu/~mills/ntp.htm

-- 
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GNU Hurd: http://hurd.gnu.org/
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Re: audio via ethernet (was: dolby digital output)

[Dan Hollis]

On Tue, 19 Feb 2002, stef wrote:
> But the problem in digital audio is that the clock has
> to be readjusted in short intervals.

I just thought of something. multicast is perfect for clock 
synchronization.

-Dan
-- 
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RE: audio via ethernet (was: dolby digital output)

[James Courtier-Dutton]

I think it is very interesting hearing what peoples views are when comparing
current digital audio technologies like SPDIF and  packet based technologies
like ethernet for digital audio.
Very few people have in depth knowledge of what is possible with both
technology.
Some people have in depth knowledge of SPDIF and sample sync etc.
Other people have in depth knowledge of packet technologies.

I will keep watching this thread to see where it goes.

Cheers
James



> -----Original Message-----
> From: alsa-devel-admin@lists.sourceforge.net
> [mailto:alsa-devel-admin@lists.sourceforge.net]On Behalf Of stef
> Sent: 18 February 2002 23:01
> To: alsa-devel@lists.sourceforge.net
> Subject: Re: [Alsa-devel] audio via ethernet (was: dolby digital output)
>
>
> Bob Ham wrote:
>
> > If it's possible for me to synchronise my PC clock to sub-millisecond
> > accuracy over *IP* on a LAN, I somehow doubt it'd be impossible to
> > synchronise word clocks over ethernet.
>
> Sounds great! 20 nanoseconds would be enough.
>
> But the problem in digital audio is that the clock has
> to be readjusted in short intervals.
>
> Anyway, which software/protocol/service do you use for
> your clock synchronisation? _very_ interesting!
>
> Thanks,
>
> Stef(an).
>
> _______________________________________________
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Re: audio via ethernet (was: dolby digital output)

[Steve Harris]

On Mon, Feb 18, 2002 at 03:11:11 -0800, Dan Hollis wrote:
> On Tue, 19 Feb 2002, stef wrote:
> > Anyway, which software/protocol/service do you use for
> > your clock synchronisation? _very_ interesting!
> 
> Probably ntp. Works well, multicast mode should be excellent for this.

It's not reasonable to compare ntp to word clock, ntp resyncs every few
minuites and works by using some incredible maths.

However, on raw ethernet, the arrival of the packets + a timestamp should
be enough synchronisation.

>From what I remeber of magic, it ensures the packets are sent
synchronosly.

- Steve  

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Re: audio via ethernet (was: dolby digital output)

[Jeremy Hall]

This one is a toughy.  Even if you use NTP, you still have a signifficant
amount of drift to deal with.  The system clock is not
sample-accurate.  Multicast NTP still requires unicast connectivity to the
multicast servers, so I really don't understand the point.

_J

In the new year, Steve Harris wrote:
> On Mon, Feb 18, 2002 at 03:11:11 -0800, Dan Hollis wrote:
> > On Tue, 19 Feb 2002, stef wrote:
> > > Anyway, which software/protocol/service do you use for
> > > your clock synchronisation? _very_ interesting!
> > 
> > Probably ntp. Works well, multicast mode should be excellent for this.
> 
> It's not reasonable to compare ntp to word clock, ntp resyncs every few
> minuites and works by using some incredible maths.
> 
> However, on raw ethernet, the arrival of the packets + a timestamp should
> be enough synchronisation.
> 
> >From what I remeber of magic, it ensures the packets are sent
> synchronosly.
> 
> - Steve  
> 
> _______________________________________________
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> 


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Re: audio via ethernet (was: dolby digital output)

[Dan Hollis]

On Tue, 19 Feb 2002, Steve Harris wrote:
> However, on raw ethernet, the arrival of the packets + a timestamp should
> be enough synchronisation.

Yes, it should.

> >From what I remeber of magic, it ensures the packets are sent
> synchronosly.

No, it just tries very hard :-) by using fixed packet lengths, and strict 
inter-packet timings.

Still, it should be adequate for most cases. And definitely more flexible 
than most current systems.

-Dan
-- 
[-] Omae no subete no kichi wa ore no mono da. [-]


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Re: audio via ethernet (was: dolby digital output)

[Steve Harris]

On Tue, Feb 19, 2002 at 01:48:48 -0800, Dan Hollis wrote:
> > >From what I remeber of magic, it ensures the packets are sent
> > synchronosly.
> 
> No, it just tries very hard :-) by using fixed packet lengths, and strict 
> inter-packet timings.

;) OK, but as long as the system is magic only they should be able to
guarantee that (modulo hardware failure).

- Steve

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