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Old 9th March 2011, 08:22 PM   #141
qusp is offline qusp  Australia
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please excuse the lack of some letter m's in my posts, the key is not working, so i copy the letter and paste it every time, a total pita and sometimes i iss one
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Old 9th March 2011, 10:18 PM   #142
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please excuse the lack of some letter m's in my posts, the key is not working, so i copy the letter and paste it every time, a total pita and sometimes i iss one
Sounds like some DIY on your keyboard is required!
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Old 9th March 2011, 10:20 PM   #143
rsdio is offline rsdio  United States
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also sabre dacs only can choose from a maximum of 2 i2c addresses with onboard mcu, there needs to be an external controller to facilitate more dacs to be controlled, however if crossover is implemented via software before titan, or within titan itself there will be no issue as they do not need to talk to each other
Two things: You're assuming that more than one DAC can share the same I2C bus in the first place, and second you're assuming that the master system should be limited to a single I2C port.

Many modern DSP chips have 3 or 4 serial ports. With high sample rates, or with limited clock rates on the DAC chips, there simply isn't enough bandwidth for a single I2C channel to carry information for more than one DAC. The solution is to separate the data onto different serial ports, and then connect each DAC to a private line. I would think that 2 stereo streams at 24/192 would be pushing the limits of a single I2C interface anyway.

I'm not a fan of Sabre, but the two address limit may be perfectly reasonable if you look at the maximum clock rate. I have designed ADC products with 1 MHz sample rates, and with a 20 MHz maximum clock rate, there simply isn't room for more than 1 chip per serial bus. The typical DAC probably allows much more than 20 MHz, but with 24-bit words the maximum clock rate is used up quickly.
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Old 9th March 2011, 10:32 PM   #144
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Originally Posted by rsdio View Post
Two things: You're assuming that more than one DAC can share the same I2C bus in the first place, and second you're assuming that the master system should be limited to a single I2C port.
From the way you've written I'm getting the impression that you might be confusing I2C with I2S. The number of DACs that can be connected to I2C depends on the number of unique addresses that can be set up. I2C is being used for control, not audio data. Hence bandwidth is not the issue you seem to think it is - the bandwidth required for control is normally very low (potentially even zero) once the DAC chips have been initialized.
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Old 10th March 2011, 01:33 AM   #145
qusp is offline qusp  Australia
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the sabre allows 2 addresses to be set within itself for dual mono and other cooperative tasks, so that each dac can be sent the same whole stereo i2s/spdif/dsd etc signal and only decode what it needs to for left or right channel, but that is as far as it goes, more than 2 dacs cannot work together like this for quad mono or whatever, without additional external hardware or software manipulation of the data stream.


yeah diy on the keyboard will be tricky, only started happening about a week ago, but its one of those super thin mac g5 keyboards, doesnt look like its going to be simple to pry apart. i've cleaned it, but sees to be an electromechanical issue underneath

Last edited by qusp; 10th March 2011 at 01:57 AM. Reason: bloody m's
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Old 10th March 2011, 01:35 AM   #146
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no, im not confused with i2s in the slightest
But you are confused about who I was replying to.
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Old 10th March 2011, 01:53 AM   #147
qusp is offline qusp  Australia
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haha, i was indeed. fixed, sorry bout that just woke up and no coffee yet, thats y excuse and i'm sticking to it. i mixed your post with his in my mind.

also rsdio, i' using a 100hz clock with my dac and i'm not under the impression that this is the limit

Last edited by qusp; 10th March 2011 at 02:00 AM.
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Old 10th March 2011, 04:04 AM   #148
rsdio is offline rsdio  United States
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Originally Posted by abraxalito View Post
From the way you've written I'm getting the impression that you might be confusing I2C with I2S. The number of DACs that can be connected to I2C depends on the number of unique addresses that can be set up. I2C is being used for control, not audio data. Hence bandwidth is not the issue you seem to think it is - the bandwidth required for control is normally very low (potentially even zero) once the DAC chips have been initialized.
Thanks for pointing this out. This thread seems to be growing fast, because I somehow missed the discussion of control, although that is very interesting.

You are correct, I was basically saying that lack of several unique addresses on the I2S port would not typically be something to complain about.
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Old 10th March 2011, 05:38 AM   #149
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more than 2 dacs cannot work together like this for quad mono or whatever, without additional external hardware or software manipulation of the data stream.
Qusp,

when you say more than two DACs, does that apply to the following situation or not?
In the hypothetical case of exa board, plus lets say three sabre boards for six channels, where each board is connected to one I2S output line (I am assuming there are 4 I2S channels from exa board) would you say that we have only one DAC or more, or in another word do you foresee the limitation you described or not?

Thanx
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Old 10th March 2011, 12:11 PM   #150
Marek is offline Marek  Poland
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exa065,

did you make any measurments of real output jitter from your device?
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