
Wireless lossless digital audio - miander
http://www.latentlaboratories.com/blog/2014/10/11/12-wireless-lossless-digital-audio
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sarreph
Awesome showcase of cross-technology signalling!

However, if you intend on getting one of these transmitter/receiver pairs, as
one reviewer on Amazon noted[1], you'll likely run into WiFi interference
problems.

[1]
[http://www.amazon.com/review/R13BSAFVTXO6H0/ref=cm_cr_rdp_pe...](http://www.amazon.com/review/R13BSAFVTXO6H0/ref=cm_cr_rdp_perm?ie=UTF8&ASIN=B00ANYXY4W)

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callmeed
So, I've recently been building DIY suitcase boomboxes (similar to
[http://theboomcase.com](http://theboomcase.com)). This is a cool hack.

FYI you can also get bluetooth-to-RCA modules for not much more:
[http://www.amazon.com/Fusion-MS-BT100-Bluetooth-Dongle-
Marin...](http://www.amazon.com/Fusion-MS-BT100-Bluetooth-Dongle-
Marine/dp/B00CUMQU50/ref=sr_1_4?s=electronics&ie=UTF8&qid=1421552046&sr=1-4&)

[http://www.parts-express.com/bluetooth-v40-audio-receiver-
bo...](http://www.parts-express.com/bluetooth-v40-audio-receiver-board-aptx--
edr-12-vdc--320-351)

[http://www.parts-express.com/parts-express-
bt-1a-bluetooth-r...](http://www.parts-express.com/parts-express-
bt-1a-bluetooth-receiver-module-for-wireless-reception-of-bluetooth-audio-sig
--320-353)

~~~
TheLoneWolfling
That doesn't solve the problems mentioned with Bluetooth though.

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fit2rule
I'm reminded of the RONJA project, which accomplishes something similar but on
a much bigger scale (and level of expense), but which nevertheless proved
quite promising:

[http://ronja.twibright.com/about.php](http://ronja.twibright.com/about.php)

As a side note, this project is interesting for another reason - its a
textbook example of a failed open source project:

[http://p2pfoundation.net/Ronja](http://p2pfoundation.net/Ronja)

.. which didn't quite hit the sweet spot for mass adoption/production, because
of a commercial fork of the project. Very interesting reading both from the
perspective of transferring high-rate data over long distances on the cheap,
technologically, and then not actually getting off the ground and doing it on
a mass level, because: politics.

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CamperBob2
Nice hack. Reminds me of the 1200-bps "modem" I built by hooking audio amps up
to the Apple II's cassette port.

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oakwhiz
S/PDIF has a parity bit, and the control messages use a CRC, but otherwise
there is no error correction. I'm not really sure how "lossless" it is, but
it's a pretty neat trick regardless.

~~~
chockablock
'Lossless' as used in the article refers to the audio compression scheme, not
the integrity of the data link.

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sanoli
Well, if you're worried about transmitting lossless high quality audio, then
that TV DAC is probably not the best. Yet it's probably just fine, where you
won't notice any difference with those speakers, so you could achieve the same
thing with a cheap FM transmitter and a cheap, used stereo.

~~~
badsock
I'm not sure I'd agree with the comparison to the FM transmitter. That TV DAC
claims to have a SNR of 90dB, which is well above the ~70 of FM radio, and
comparable to "CD quality" (modulo marketing BS).

That being said, the benefits of 24 bits over 16 (which I'm not convinced of
in any case) would certainly not survive that setup.

~~~
smoyer
I was in the cable industry for over 20 years and am well acquainted with NTSC
... I suspect the audio quality at 6 MHz to be far better than an FM signal
which is nominally 100KHz wide. The FM system is more resistant to amplitude
changes (due to distance, etc) but can't encode as much data as the VSB-AM
signal used by NTSC.

There are a few caveats and I haven't looked at the transmitter/receiver pair
he purchased. If it's simply 6MHz of bandwidth transmitted for some specified
distance, it will probably work. SPDIF is a digital signal and while it runs
at 6Mbps, there are significant harmonics that can be passed through the
fiber. Since we can assume the first harmonic will pass through the link, you
can expect a signal which has more sinusoid pulses coming back out of the
receiver. With a PLL to recover the clock and a good data recovery circuit
added to the receiver, I'm guessing he could easily push this link to 50 to
100 feet.

As an aside, the NTSC signal is actually sending far more information as a
whole and while it uses an AGC to overcome amplitude changes during
transmission (the sync pulse is adjusted to be -0.3V), it also uses a comb
filter to recover chroma information and the luminense is AM modulated above
at the pixel clock rate. Your eyes are actually pretty low resolution compared
to your ears and there are lots of ways to fool the brain's image processing
(e.g. interlace makes a 30FPS system look more like 60FPS).

In any case, a very creative build!

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lttlrck
I did that about a decade ago and got around 20 ft if range through two walls.
Of course the transmitters were a bit more expensive back then. It worked well
enough and I was enormously pleased with myself :-) but occasional glitches
were very annoying, I never tracked down the source, reducing the distance
didn't help. It was likely some sort of EMF interference
(refrigeration/microwave/wifi etc).

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headShrinker
Apple AirPlay while lossless, is limited to 16/44.1. It's really a great
option for wireless transmission and it uses wifi not bt. It's not 24khz so it
will never be considered a pro audio solution but wireless and very
functional, it is.

~~~
foxhill
"limited" to 16bit 44.1khz? that's the sample rate and bit-depth you get on
CDs. and it has been A/B tested to death - higher bit rates and sample rates
have (at absolute most) little to no discernible impact on sound quality -
AirPlay is more than enough.

"pro audio" uses 24 bits for sample storage, so that the noise floor remains
inaudible after processing has happened to each track. 16 bit output is more
than adequate for monitoring.

~~~
jdietrich
Pro audio uses high bit depth throughout the signal chain to simplify gain
staging. 16 bit is just barely adequate for normalised signals, but it is
inadequate for signals of unpredictable level as it leaves no room for error.
Set your gain too high and you get clipping; Set it too low and you raise the
noise floor. You never need 120+dB of dynamic range, but it is incredibly
useful to have 30dB of headroom to cope with sudden increases in level _and_
an inaudible noise floor.

This extra headroom is critical for digital systems, as they have no headroom
above 0dBFS - most analogue devices distort progressively (and often rather
pleasantly) when pushed too hard, but digital clipping sounds horrible. Once
you've run out of bits, all hell breaks loose.

16 bit is absolutely fine for domestic audio, but it is totally inadequate in
a production environment. Without the extra dynamic range provided by 24 bit,
you're stuck with some kind of compromise - either you risk overs, you raise
your noise floor, or you have to stick limiters in front of all your ADCs and
put up with your peaks getting squashed.

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Grazester
$12 for the wireless transmitter but the total for the other things needed to
make that $12 transmitter work is $164. cool none the less.

~~~
anigbrowl
Anyone who does pro audio usually has one or more S/PDIF interfaces sitting
around gathering dust, it's still the default standard for stereo digital
transmission.

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song
Great, I'm going to test that :-) The delay with a bluetooth setup is very
annoying...

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dharma1
love it.

