Alternative encoding and CD player with I2S

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Alternative encoding and CD player with I2S

Postby kareno » Thu Jan 19, 2012 11:08 pm

Over last summer I hoarded little 5" TVs which I bought from car boot sales (you can pick them up for one or two pounds). I have used one of these to make a CRT NBTV monitor (more on that another time).

One of the TVs had a CD player built into it. Or so I thought - the CD player was detachable and docked with the telly. More interestingly, this CD player is based on the Samsung chip set which makes audio available internally as a serial digital data stream (I2S format)!

Since that discovery I have been thinking about getting a PIC to deserialise the left channel data in one of two ways:

1. A 2xOversample mode in which each left channel sample holds two 8 bit video samples so that replay can be at the higher rate of 88.2kHz - adequate for 60 lines.

2. A 'high colour 16' mode which produces RGB by chopping the bits up in the ratio 5:6:5 (green getting the extra bit)

I just wondered if these were any kind of standard in NBTV work? It would be nice to think I don't have to produce a load of data preparation software again.
kareno
 

Postby Steve Anderson » Fri Jan 20, 2012 12:20 pm

I do recall that Klaas and others did de-serialize the data stream from an audio CD...remiss of me to forget the others involved. I think it was mainly to do with colour. whereby the lesser bits where used for the colour-difference data.

I'll have a dig around and see what I can find, it may well be in a past issue of the newsletter.

Klaas, of course you can point Karen in the right direction.

Steve A.
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Postby gary » Fri Jan 20, 2012 1:35 pm

'Twas Vic Brown - in relation to the Robers-Brown colour format.

Edit: I should say though, that as far as I am aware, that is just in relation to the decoding of a standard s/pdif stream, which is the consumer version of the AES format (same except for being unbalanced and different voltage levels, I think). The data itself is the same as is encoded into the colour format wave files. This is an NBTVA proprietary format (for want of a better description).
gary
 

Postby kareno » Sat Jan 21, 2012 1:11 pm

Hi Gary,

Oooh, do tell me the format of colour NBTV wave files :)

If it's too complicated to explain in a message such as this that's okay - if it's that complicated I'll probably go my own way re coding method anyway.

My only worry about chopping up the bits like this is that little box labeled 'interpolator' in the DSP chip's block diagram. It seems that it fills in with interpolated values if it detects a corruption. That'll work great for sixteen bit samples but won't work at all well when the bits are arbitrarily chopped up.

I've worked out how to get a PIC to deserialise the data and present the left channel's sixteen bits on GPIO pins. Should be my shortest program yet!

My hope is to end up with a multipole connector on the back of the player sporting RGB and right channel audio out. I will still be able to use line out for normal monochrome 32 lines of course.
kareno
 

Postby Steve Anderson » Sat Jan 21, 2012 4:09 pm

I found the item I referred to above, it's in Vol. 31 No. 2 of the newsletter entitled "Composite Colour NBTV on CD (CCNC)" by Klaas Robers and Vic Brown. (December 2005).

A copy of this can also be found on the Club Newsletter back-issue CD.

Now, with good reason I feel obligated not to forward the item on as the following is within the introduction of every copy of the newsletter on the CD...

"Don't deprive the NBTVA of income to keep subscriptions low. Please don't make illegal copies. You may make one copy for your own use."

At fifteen quid for so much data and world-wide delivery, it's a raving bargain!!

Steve A.

Later...Viewing my own scan of the same issue of the newsletter, the item in question is totally different! Same subject, same Vol. No. but only credited to Vic Brown....something's not quite right....but it's probably me.

Later yet...It is me, there's actually two items on basically the same subject within the same issue of the newsletter...both worth reading of course....
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Postby kareno » Sat Jan 21, 2012 10:48 pm

I have the back issue CD, Steve. As you say, a fantastic bargain.
kareno
 


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