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Old 1st June 2011, 12:46 AM   #11
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you could change the code so that it writes the binary mask value instead of PULSING the mask out. that would be the only difference. it would probably cut the amount of code needed by removing a good 50-100 lines, making it even simpler!

what I didn't like about regular relays is that they require higher power due to the fact that they are voltage-on to activate them. but they are MUCH easier to buy, that's for sure!
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Old 20th October 2011, 11:44 PM   #12
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today I created an AES3 output on the spdif switch. or, something close to it, at least not a re-encode of the bitstream but just a more 5v-based balanced output.

all I had to do was take a ttl level output from the switch chip. I used a 74151 that has both a Y and ~Y output, so use one for opto out and one for the next stage, the AES3 out. spdif doesn't care about bit polarity at the raw 'wire' level so its fine.

next stage is a 75als191 (or ua9638) rs422 line driver and a pulse trafo. from the 75191 I used a series R (50-200 ohms, not too critical in actual practice) and then the pulse trafo. ideally a 1:1.2 ratio to match 75/110 would be best but to be honest, I doubt I have anything like a real 75ohms off my ttl switch chip I did have a 110R in parallel with the secondary of the pulse and then that went to the twisted pair and off to the DCX2496, which was my ultimate target for the spdif switch.

things work fine. it costed a driver chip (8pin dip), an inexpensive pulse transformer ($3 or so) and an R or two. plus whatever jack you want to use (I could only fit a 1/4" TRS jack but luckily there are common TRS-XLR cables and I used an existing commercial audio cable).

I can't speak about jitter in this build (hand made proto board stuffed in suboptimal plastic chassis) but I'm not hearing any sound issues from the DCX (my only aes3 box in the house I can test with).

I'm getting closer to making a PCB. will update the thread if/when that happens.
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Old 24th October 2011, 10:12 AM   #13
qusp is offline qusp  Australia
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you used a 1/4" to XLR for AES3? haha, shows how hardy it is. doesn't matter really, XLR isn't close to 110R either, the whole 'balanced' AES standard is a bit of a shmozzle imo
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Old 24th October 2011, 10:18 AM   #14
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I seem to have luck with spdif. wiring never seems to be critical and receivers always lock on. I know, I know, the impedance gods will curse me for saying so. the audio sounds fine to me and no matter what I do, it never gets better or worse.

the proto was also just hand wired; but again, spdif seems to just plain work no matter what wire or connectors I use.
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Old 22nd February 2012, 10:41 PM   #15
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update: I may add something like this to my spdif switch display. its the spdif sample rate that is directly read off of the decoded i2s LR-clock line. here's my test bed that has the wolfson wm8804 spdif receiver; then it splits out i2s to a 3wire ribbon cable going to a test junker dac (not relevant here). the red highlight shows a schmitt trigger on the word clock that feeds my arduino (to a spare digital-in pin). the arduino does a software frequency counter trick and shows the value it counted. I did 2 test runs to see how close the software freq counter was to my good one. it was good enough so that I can truncate some digits and show the native rate. (I'll test at 96k and higher when I get a chance).

Click the image to open in full size.

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I've been wanting to do this for a long time but it always needed an spdif receiver. so, when I built one up for another project, I decided to revisit the SR display problem again.

it came in handy, already, too; I found when my sound card was sending movies out at 44.1 and music at 48k I had to use ASIO to get my sound card to be native at 44.1 again. I never knew this until I just checked. the device already made itself worth its effort.
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Old 27th February 2012, 06:11 AM   #16
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more progress.

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and a really stupid and boring video demo of it:

http://www.netstuff.org/spdif/spdif_led_meter_1.mp4

this started out as just a test tool, but I'm wondering if its got potential as a small purpose-built spdif rate-meter on its own. its very low cost and uses a 168 or 328 series arduino and some misc junk r/c parts you have lying around.
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Old 27th February 2012, 03:06 PM   #17
zinsula is offline zinsula  Switzerland
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Hi linuxworks, do you plan to software control the WM8804 with LCduino?

As far as I understood, your aim is not to switch S/PDIF between sources and to convert it to I2S, but to switch and to hand it over to the next processing step. Am I correct?
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Old 27th February 2012, 04:41 PM   #18
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yes, I do plan to have software control for the 8804/8805. its mostly coded but I have not gone beyond 'it compiles'. I plan to get back to the software driver for it, though.

the only things I want to use i2s for are for getting the samplerate via decoding to lr-clock; and if its convenient, I'd like to throw in a small dac chip just because the i2s lines *are* there (grin). I tried a pcm5102 and was not impressed. same with the ESS equivalent dac chip. I'm going to try a few more 'easy dac chips' but this is not a focus and not meant to be a replacement for a proper external dac.

its true that I want to stay spdif in and out. whether its 'the best' data transport for digital audio is not my call to make; the fact is that lots of gear use spdif and having a remote controllable hub to switch them is useful, I think.

for the cost of 1 switch gang, I found I can provide two and give 2 buses for output, independant of each other. a use-case is a 'monitor' out and a 'record' out. each switch input gets a buffered copy of the stream and each switch is addressible on its own. the rest is up to the main processor; its that guy who takes the user request such as 'play my squeezebox' and it knows that its on digital switch #1, port #3 and we have to route thru analog-in #5 on the preamp. all that lookup-table work is taken care of by the main lcduino and the switch just gets told to set its A gang to 'a' and its B gang to 'b'. and if there is a dac chip onboard, I'd tie it to one of those switched outputs and give the user a line-out in addition to an spdif-select-out.
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Old 27th February 2012, 05:14 PM   #19
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Thank you. I'll stay tuned, especially on your WM8804/8805 work.
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Old 27th February 2012, 10:33 PM   #20
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integrated the samplerate display into an existing DAC:

Click the image to open in full size.

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so far, the proof of concept works! I found that my sound card was not even set to 48k for movies, for some reason. everything was being resampled to 44.1 (isn't THAT a switch, lol!). I found the sound card setting, changed it and now music comes out at 44.1 and movies at 48k (stereo downmix). it already earned its keep this first time I used it.
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