Wireless lossless digital audio

http://www.latentlaboratories.com/blog/2014/10/11/12-wireless-lossless-digital-audio

by miander • 12 years ago

94 22 12 years ago

sarreph• 12 years ago

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...

Grazester• 12 years ago

$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.

Nexxxeh• 12 years ago

If you don't already have digital coax in on your amp, and digital out on your soundcard?

I don't think I'm unique in having both?

anigbrowl• 12 years ago

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.

dharma1• 12 years ago

love it.

sanoli• 12 years ago

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• 12 years ago

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• 12 years ago

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!

song• 12 years ago

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

CamperBob2• 12 years ago

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

oakwhiz• 12 years ago

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• 12 years ago

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

callmeed• 12 years ago

So, I've recently been building DIY suitcase boomboxes (similar to 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.parts-express.com/bluetooth-v40-audio-receiver-bo...

http://www.parts-express.com/parts-express-bt-1a-bluetooth-r...

TheLoneWolfling• 12 years ago

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

fit2rule• 12 years ago

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

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

.. 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.

lttlrck• 12 years ago

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).

headShrinker• 12 years ago

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• 12 years ago

"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.

WhitneyLand2• 12 years ago

16 bit is not just adequate it's optimal. It's enough for perfect sound, unless, as you point out, you are editing.

Disappointing this pseudo science makes it on to HN.

There was a nice article here a while back that went through the entire subject in depth, can't recall the site.

jdietrich• 12 years ago

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.

lukifer• 12 years ago

AirPlay is great, but it does have a non-trivial delay while it syncs and buffers, which becomes especially noticeable when skipping tracks.

WhitneyLand2• 12 years ago

Yes, Apple really needs a low latency protocol for both audio and also AirPlay video. Would essentially enable any device to be a game console.

Wireless lossless digital audio

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