Revolution?: HDMI ARC, eARC and S/PDIF

The move from S/PDIF to HDMI ARC failed in bringing even a small revolution, but the introduction of eARC in HDMI 2.1 may now actually allow a major revolution.


  • S/PDIF: History
  • Audio Return and Directional Audio/Video Cables
  • Pre ARC (before HDMI 1.4, 2009 )
  • HDMI 1.4 with ARC (Audio Return Channel)
  • Sonos Beam – ARC at work!
  • TV: A HiFi capable Digital Pre-Amp?
  • eARC – HDMI 2.1 (2019)
  • The Audio Revolution

S/PDIF: History

The traditional way to send digital audio within HiFi, has been the S/PDIF coaxial or optical connection.  The connection originated from the desire to send digital information from a CD player to an amplifier, in order to use the D/A conversion within the audio amplifier.  The system was designed to send stereo signals of CD resolution, but within that design has also been able to send compressed surround sound.

Audio Return and Directional Audio/Video Cables

An important concept to have clear before discussing Audio Return Channel, is that audio and video cables always (or almost always) have a direction.  One end of the connection will act as an output, and the signal is sent to the other end which will act as an input.  Even though the connectors on each end of the cable are the same type of connector, there is a different role for each end of the cable.

So an RCA connector from a CD deck to an amplifier connects the output of the CD deck, to an input on the amplifier.  With a tape recorder, there are output connections for when a tape is in playback, and input connections for when a tape is being recorded, and the same pin type is used for each end.  With RCA cables, two sets of red and white leads, one set from the outputs of the tape player to the a set of two inputs on the amplifier, and an identical cable confusingly carrying signals in the opposite direction.  To simply things, there was a ‘DIN’ plug with 5 wires. A ground level, plus and left and right signal for one direction, and another left and right signal for the opposite direction.  Of course, if you tried to use this cable to connect to tape recorders to copy a tape…. the two inputs were connected and the two outputs were connected, so it would not work.

The point is, that every wire in an audio/video cable has a direction: either input or output.  Normally, all HDMI ports on a TV are inputs, and all HDMI ports on DVD players are outputs.  In fact, even DVD recorders have normally have all HDMI ports as outputs, and a different system for video inputs.

So if all HDMI ports on a TV are inputs, how does the TV output anything?  An Audio/Video amplifier, or a centre speaker, need sound output from a TV when TV programs are being watched.   The sound and video are inputs to TV during a DVD, but the sound is an output when watching live TV, so while video is always ‘in’, audio can be in or out.

Pre ARC (before HDMI 1.4, 2009 )

Without ARC, the answer is to have a separate audio connection running back from the TV to a speaker or Audio using SPDIF.  Of course, SPDIF was designed for sound that does not have control, so even with a centre speaker, the speaker will need its own volume control.

HDMI 1.4 with ARC (Audio Return Channel)

Recall that ‘DIN’ plug for tape deck connection?  Both in and out in the one cable.  HDMI 1.4 decided to use the same concepth with ARC.  ARC adds the audio reverse direction to the HDMI cable, so now and HDMI cable can be thought of a Audio and Video going in one direction, plus audio returning in the other direction. However while the audio and video sent to the TV have no control information (volume or tone for Audio, brightness or contrast for video), the return audio that has been added to the specification  does have added control information.

This added control information is extremely important. This cable, for the first time,  provides control information with a digital audio signal.  This gives the return direction of digital audio additional uses that the ‘normal’ direction of HDMI audio does not have.

The problem with ARC, is the specification was too flexible, which has allowed different interpretations, which leads to interoperability problems. The problems have led to a common suggestion being “avoid ARC, it is too flaky”.

The Sonos Beam – ARC at work!

Sonos has become a major brand. In wireless multiroom, the Sonos is the clear industry leader.  Which means Sonos introducing a sound bar with HDMI ARC as the only input, creates pressure on the major TV brands to get their ARC actually working properly.

When working properly with ARC, the Sonos Beam gives a preview of the revolution that will be fully enabled by eARC in HDMI 2.1

The Sonos sound bar being designed ARC is more significant than it sounds.  The significance is that by using an digital source which has control information already present, the Sonos beam does not have to act as a digital preamp.  The Sonos Beam can concentrate on converting digital to analog, amplification and being a speaker.

That difference may appear subtle, but in reality it is a revolution.

A pre-amp selects which input is to used and controls volume etc.  Most soundbars try and take over the function of being a digital pre-amp, which is why they, duplicate the multiple HDMI inputs that are on the TV.  Many will even have host an app store, because most digital sources have moved to being through the web, so to select these inputs you need to have app store. Then, even though the TV has a volume control, so does the soundbar, and when moving the soundbar you need to switch app stores.

None of this is needed when relying on ARC.  If ARC actually works properly, the TV can be digital pre-amp, leaving a single app store, and a single set of inputs. Nothing else changes when you turn on the soundbar other than the sound quality.

What Changes When Relying on ARC?

Using S/PDIF, the alternative to ARC, means no control information.  With no control information, the signal must enter a ‘pre-amp’ or ‘control-amplifier’ stage, even though the TV already has, in the digital domain, perfectly adequate control amplifier capability.

Samsung TV connections (2018)

Note a smart TV has a volume control, an app store as well as physical HDMI and usually other inputs. A sound bar repeats (see below) repeats most of these connections.

Yamaha YSP-5600 sound bar connections

The Sound bar does add analog audio connections, plus an HDMI output for connecting the TV, but otherwise the sound bar generally repeats the connections that were on the TV. This means to use the sound bar as designed, you must move all the connections from the TV to the sound bar, then use the sound bar to select inputs.  Unless the input is from an App such as Netflix, or Spotify….. oh wait there is a Spotify app on the sound bar also, but not a Netflix app.  Confused? So the sound bar has its own remote, connections and apps, so when not relying on ARC, you get two remotes, two sets of input connections and two sets of apps.  But if you rely on ARC? One remote, no duplicated connections or Apps spread between two different app stores.

Connections when relying on ARC

TV: A HiFi capable Digital Pre-Amp?

Consider a digital preamp that accepts digital data in, and sends digital data with control information out.  This means a digital pre-amp that does not actually amplify, as digital signals are not amplified. The actual amplification must happen after a signal is converted to analog, in other words after a DAC.  Dealing with analog signals and retaining hi fidelity is the domain of high end HiFi, but while the signal stays digital, it is purely about computing.  TVs can have high powered CPUs, and can do digital. This means provided the Analog processing is handled externally to the TV, a TV can perform the digital part of processing the signal.  That means retrieving the digital information from the net with an app, or simply routing the input stream from a DVD or other device through to the output.  For all cases, simply adding an additional information source of playback settings such as desired volume, or other information the external HiFi ‘digital power amp’ will use in the real HiFi task, turning bits into sound. What a TV as a digital pre-amp should not do, is try to be an analog pre-amp as well and process analog inputs.

eARC – HDMI 2.1 (Nov 2017)

The original ARC introduced back in 2009 was a typical first try. Things were not perfect. Firstly, the new specification had so many optional elements that implementations vary too significantly for a real standard. Secondly, the bandwidth for the digital signal, although an improvement on S/PDIF, was not sufficient to handle multichannel or newer object based advanced sound encoding. Thirdly, the control channel information was best provide by the ethernet data, but ethernet data was optional in the standard.

The HDMI 2.1 specification mandates eARC.  Nothing required for eARC is still optional.  The bandwidth available copes with all current codecs, and there is room for the future as well.  Ethernet is no longer optional allowing more robust control information, and evolution of control specifications.

The Audio Revolution

In simple terms, once HDMI 2.1 is the normal, and thus eARC becomes common in homes, you could design a ‘Sonos Beam’ alternative that works as simply as the Beam, but with the clarity and perfection of the best HiFi systems, both for audio, and for Audio/Video.   That is, using the inputs and of the TV, the remote of the TV, and app store and source selection of the TV, but with multiple speakers and amplification optimised for HiFi and/or Home Cinema.  Sound  delivered with the sound qualify of the highest end home theatre or HiFi system.  HiFi and high end home theatre as simple as the Sonos Beam.

What about sources that do not connect to TV?  There are questions left unanswered by this post.  The answers do exist, they are just too long for this one post, and I will add these answers in other posts.


Finite World: Finite vs Unlimited.


Finite: What does ‘Finite‘ actually mean?

The Key: Not Just Two Possibilities, but three.

Even in a mathematical context, there are three possibilities:

  1. Finite.
  2. Infinite.
  3. Undetermined.

Depending on context, infinite and undetermined can be equivalent, and in both cases, you not aware of any limit. Something only becomes ‘finite’ when you become aware there is a limit.

Dictionary Definition Of Finite: It depends on context.

While ‘finite’ and ‘infinite’ have mathematical definitions, dictionaries reveal that common usage extends beyond the mathematical definition. The dictionary definition of infinite includes “immeasurably or inconceivably great or extensive : INEXHAUSTIBLE” as well as “subject to no limitation”, and for finite we have “completely determinable in theory or in fact by counting, measurement, or thought” .

By example, as a human we can consider the number of times a person in the open can breathe as being infinite, even though the amount of oxygen in the air is finite so there is a theoretical limit, a person can breath ‘an inconceivably large number’ and still have no noticeable impact the level of oxygen.

The Working Definition of Finite for this context.

The meanings of finite and infinite depend on context, as outlined below, so to avoid ambiguity, in the context of these pages, ‘finite’ means:

Finite: ‘known to have a limit that could, in practice, conceivably be reached’.


So yes, words have different meanings depending on context, but it this context, unless explicitly prefixed such as ‘theoretically finite’, ‘finite’ will mean with a known and potentially constraining limit.

Given the principle there are three possibilities, they become:

  1. Finite: known to have a limit that could, in practice be reached.
  2. Infinite: it is known the that limit cannot in practice be reached.
  3. Undetermined: there may be a limit, but if so, the limit has never been reached.

I would suggest that human nature is to assume that when the limit cannot be determined, then it will not in practice be reached, which means infinite and undetermined are seen as equivalent. In this context, the opposite of finite because ‘unlimited’.

Unlimited: Unconstrained by any known limit.

Again, me.

Again, words have different meanings depending on context, but it this context ‘unlimited’ will without any known constraining limit.

Finite World: When the world of humanity progressed from ‘undetermined’ to ‘finite’.

To the first people on Earth, it must have seemed that no resource was finite, virtually nothing had any known limit. It is not that people believing things infinite, it is that numbers seemed unknowable, and undetermined seemed equivalent to without limits.

There were always new lands to be discovered, hunting animals did not noticeably impact their population, nor did gathering fruit and vegetables make an impact. Fishing did not noticeably impact fish populations.

Most things remained finite until around 1650 CE. At that time no individual even knew of all the continents on Earth making even the amount of land seem unlimited. Sustainable was not a concept people needed to contemplate, as it seemed every thing humans did was inherently sustainable.

Fast forward to the 21st century and there has been a population explosion dramatically increasing the number of humans, and an industrial revolution increasing the impact individuals have on the planet. Now, most people see ‘sustainable’ as essential, but in surprisingly many ways, there are still people who do not, deep down accept the Earth is finite, and sustainability is essential.

Finite World and Sustainability: It is all relative.

Nothing is sustainable without constraints. Every ‘sustainable’ practice is only sustainable within limits as to the number of people who can engage in the practice and the length of time it can continue. In practice, ‘sustainable’ means ‘more sustainable’ rather than absolutely sustainable. Even ‘sustainable’ farming has a limit to the scale and thus the number people it can feed, and on a planet with a finite life, cannot exist forever.

A question becomes, to be ‘sustainable’ how many people can be supported and for how long? As an extreme example, even breathing air has a limit to the population size before it become unsustainable. There is always a window.

Some people see perpetual population growth as sustainable, and within a sufficiently small window of time it is sustainable. Others see burning fossil fuels as sustainable for as long as 50 years, and in their eyes that is sustainable, while younger people, of people who care about younger people, may require a longer time to be sustainable.

Then there are others who an in denial. Prior to around 1650 CE, everything seems sustainable, and it worked for so long then the same attitude can work today.

What really killed the dinosaurs?

485176_441599455926469_1655029236_nWhile I do literally mean the actual dinosaurs, there is also a lesson in the answer for the metaphoric dinosaurs that big companies can become.

“A giant meteorite wiped out the dinosaurs” is the catch phrase.  But have you ever wondered “why the dinosaurs, when so many other animals survived?”.  The alligators survived, fish survived, mammals survived, even other reptiles survived, and even frog species that seem so sensitive to any change in environment survived that meteorite.

So why the dinosaurs?  And what is the lesson? These answers after first some background and myth-busting. Continue reading “What really killed the dinosaurs?”

The ‘perfect’ everyday bag: messenger bag, shoulder bag or backpack?

Not everyday bags

I am on the hunt for the perfect bag to carry things with me, but is this a backpack, a messenger bag, or some hybrid of the two. The strongest candidates right now, are the peak design backpack, or the ‘urban disguise’ series from Thinktank. Peak design make a messenger bag the can work as a backpack, or a messenger bag like backpack, but there is not a single review I have found evaluates use of the backpack as a messenger.  Given how frequently I see people with backpacks slung over one shoulder, surely someone else cares about how a backpack performs in messenger mode? The perfect bag? John Steed and the Avengers? All will be revealed! Continue reading “The ‘perfect’ everyday bag: messenger bag, shoulder bag or backpack?”

No new Surface ‘Pro 5’ after all?

Lots of others ‘crystal ball gaze’ into the future of Microsoft’s ‘Surface’ products. Here is another perspective. A lighter tone than the usual post, here is a look at both what Microsoft are likely to do, and what they should do. 🙂  Ok, it is largely crystal ball gazing, but so it seems is every other prediction on the ‘Surface Pro’, so here is a different perspective.

1) There may be no ‘Surface Pro 5’, as a name change really makes sense.

Since releasing the original ‘Surface’ and then ‘Surface Pro’, the ‘Surface product line’ has evolved to a point where the original names are in serious need of review. Which is the most ‘professional’ product of the current range? The ‘Surface Pro’, the ‘Surface Book’ or the ‘Surface Studio’?   The ‘Surface Pro’ was ‘Pro’ relative to the original ‘Surface’, and the two names made sense.  Now ‘Surface’ is a family and ‘Pro’ does not describe where the ‘Surface Pro’ fits in that family.  How about ‘Surface Tab Pro’ or ‘Surface Pad Pro’?  Microsoft can afford to pay people to come up with a better name, but a new name is needed.

2) Two new products, one Qualcomm based, one Intel Based!

“We need to be willing to lean in to uncertainty, take risks and move quickly when we make mistakes, recognising failure happens along the way to mastery,” Nadella wrote in a 2015 memo to Microsoft employees

So what will be the new ‘non pro’ device?  The philosophy of the ‘Surface’ products is to do things differently and take risks. Innovation. But as the most successful product in the Surface line-up, there is a limit to the risks that can be taken with the Surface Pro.  Which is why, beyond the logic for the name change, there will logically be a new Kaby Lake CPU based device to follow on from the Surface-Pro.

Contrary to other suggestions, the USB-3 port should stay, and instead the mini-display port should upgrade to Thunderbold-3.  Re-chargeable pen, improved battery life, incremental improvements.

3. The ‘Surface’ replacement, the bold step!

This is where the room to take risks exists.  The recently demonstrated ability to run full windows on a Qualcomm CPU opens the door for something new, lighter and with LTE connectivity.  Such a device would be the logical reason for display at MWC 2017.  Running full windows on such a CPU enables a phone, but this new device needs to be another leap, and something targeting both phone and tablet is the logical solution.  Phones today are ready for the next step, with so many people using hands free or earphones/headphones, do we really need a device designed to be held to our head anymore?

How the ‘basic income’ proposal could change society

The current wealth distribution system is an already a broken system about to face severe attack. As discussed in Robots & Job Terminators, the role of employment is set to change.

canada20flagflagbigfinlandOn engadget, the post How will you survive when the robots take your job? outlines the ‘basic income’ proposal, as put forward by many in the tech industry and being experimented with in Canada, Finland and the Netherlands. This articles provides a great starting point and conveys the basic idea and if unfamiliar with the idea it makes sense to read that article first. This post is about looking further, in terms of thoughts about what else should change if a ‘basic income’ is introduced and what would be needed to make such an idea work. What would such a measure cost, and what would be the impact on society of a total package, of a ‘basic income’ together with a logical set of policies to create a total package? Continue reading “How the ‘basic income’ proposal could change society”

Australian Record Trade Surplus: good news, or a warning on automation?

skitched20truckAs explained by ‘Alan Kohler’ of the ABC, the record trade surplus is largely due to “A huge rebound in iron ore, coal and gold exports delivers a record trade surplus of $3.5 billion in December, providing a big boost to national income.”, with no proportional increase in imports.

I suggest an analysis of the impact on the Australian economy is reason for people around the world to consider the impact of automation.

Continue reading “Australian Record Trade Surplus: good news, or a warning on automation?”

Highlander Economics: Does it end with only one?

from IMDB

Back in 1986, the movie Highlander was released. It was actually sufficiently successful to inspire four sequels, plus spin offs and even a reboot. Something in the original clearly stuck a chord, and the tagline and concept ‘in the end there can only be one’  could be part of this.  The plot centres around a small group of individuals, immortals, who become ever stronger by defeating ‘competitor’ immortals in mortal combat.  The immortals all seem have a share of power. Defeat another immortal and grow stronger as the victors gain the power of the vanquished, until only one immortal remains, and the one remaining will hold all the power.  So how closely does the ‘rules’ of the highlander actually match the ‘rules’ for competitor companies?

How accurate is the analogy? Continue reading “Highlander Economics: Does it end with only one?”

The Canary: part II

typewriter2My previous post was a diversion for the usual, and this post is a continuation of the diversion, but normal topics are set to return!  For now, a little more the episode of the early warning of failing journalism.

In the previous ‘canary post’ I outlined reasons why the almost universally reported ‘Microsoft will not release new Surface Devices because they have to wait for the new Intel processors’ at least from my analysis seems an example of the press simply getting in wrong, as the processors concerned are actually well know to be already available. (example of reporting here: note the words “because it’s too early to put Intel’s next-gen Kaby Lake processors and chipsets into the devices” and here and here. And this is reporting after the even has announced.  Before the event was announced there was even stronger repetition of the clear error. Over and over.

If the press can get something as simple and as obvious as this wrong, what else can they get wrong?   Most disconcerting in a society that requires a functioning press for the protection of democracy. After further analysis of what is misreported, I will look at just what are the possible reasons for this misreporting.

Back to the innocent little canary, the misreporting of the environment for a tech company to release new products.   As of today, October 16,  an actual Microsoft press event is now scheduled for October 26, and yesterday,  the first signals that my analysis which just two days ago ran contrary to almost all press reports, may indeed be correct.  That evidence is that Amazon now lists current surface products as ‘(OLD VERSION)’.  Now finally there are journalists suggesting that this may be due to an update of current surface models to the new Kaby-Lake cpu. This is yet to be confirmed, so stay tuned for confirmation.

There is also a second part of this story.  Journalist predictions were in two parts:

  1. current surface products cannot yet be updated as they must wait for the new CPU
  2. instead a new ‘all-in-one’ surface desktop will be released

It has already been discussed that in fact the currect surface products do not have to wait for the new CPU as the ‘mobile’ versions of this CPU are already released.

The important point for ‘part 2’, the release of the all in one, is that this idea is impacted by the fact that the desktop versions of this new ‘Kaby-Lake’ cpu are in fact not available.  Despite the mobile new CPUs actually being available and the Desktop versions not available, all the reporting was the mobile devices cannot be released and no discussion at all on the need for the new CPU in a desktop.

Microsoft may be about to announce a new ‘all-in-one’ device, but the lack of new desktop CPU being available means either:

  1. the new ‘all-in-one’ device will be announced but not available until next year
  2. or this new ‘all-in-one’ will actually function like an ‘all-in-one’, but actuallybe something different and be more a modular system and allow a choice of using current surface devices for CPU and disk, or offering a CPU and disk drive as a separate module.

I can add more at a future date, but this is probably enough discussing of this now to illustrate the point, and refer back to in a future post it this turns out correct.


It is only about laptop computers, and I am only interested because I wish to buy one by a specific date for a present, so just waiting is not appealing. But the significance of what is clearly an error that could be discovered with even the research available to an outsider, being reported and echoed throughout the press is a great concern.  Is this also happening with respect to the war in Syria for example.  Or reporting on the candidates in an election?  I feel the age of the internet has eroded the business model of journalism, and we all may pay the price.  More news, but the same news repeated without any fact checking.

Surface Pro update: Canary for the problems in journalism?

typewriter2Ok, so this post is about what is happening with updates for the Surface Pro and the Surface Book, but is also about the problems in technology reporting, which themselves are symptoms of a wider problem.

Firstly, to the Surface Pro/Book.  There are lots of rumours of an update, and rumours there being rumours is understandable, but the rumours seem to all contain the same conclusion, despite logic to the contrary.  Why the continually repeating the same mistakes, and missing key points.  I mean, one person making an error….ok.  But so many websites repeating the same errors?  What is going on? Continue reading “Surface Pro update: Canary for the problems in journalism?”

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