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Old 18th March 2014, 01:31 AM   #1
YashN is offline YashN  Canada
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Thumbs up Need advice on a small DSD DAC experimentation platform.

I am bent on getting a board or a few if needed to build myself a small tinkering platform for DAC experiments. Based on what I understand for now, it looks like the power supply or supplies will be very important, a USB-2-I2S interface as well.

I may experiment with or without DAC chips: for instance, I would like to play with the DSD bitstream and filter it passively for a start.

The thing is: I'm not sure if for example just getting an Amanero or similar interface suffices for me to tinker with or if I need to add additional boards.

In the future I would certainly like to tinker with multi-channel DSD as well and perhaps even do some digital operations on the bitstreams, so for this, I am planning to look into affordable FPGA boards.

I already have high-res and DSD material, including the software to do bit-perfect output through asynchronous USB (I'm using Audirvana+ on a Mac, which I love to bits).

Let me know your thoughts, gentlemen. Thanks.
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Old 18th March 2014, 01:46 AM   #2
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I haven't played with DSD myself although I did attempt a 'discrete' version of Philips' TDA1547 many, many years ago.

My thoughts would be 1) jitter is going to be a major problem and 2) use an LC filter, at least 4th order.

To address 1) I'd suggest going for an analog FIR filter by using a shift register as delay line and summing the outputs. I believe Bruno Putzeys is using something similar on his PWM-based DAC.
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Old 18th March 2014, 02:56 AM   #3
YashN is offline YashN  Canada
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Thanks for the pointers, Abraxalito. I'll certainly also use an external clock and experiment with jitter-reduction with or without an FPGA board. That analog FIR Filter is intriguing.

I've been doing some head-scratching research on a board by ST Micro, and right after posting, it seems I could even get it to some USB-2-I2S, not that I'm anywhere near being able to code that tonight, but heck, I want to try

Actually, having seen the PS Audio technical presentation by Smith, I think dabbling in proper PCM decoding could be a worthwhile pursuit, even with RedBook.

My main interests though remain DSD, multi-channel as well as integration with tubes.
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Old 18th March 2014, 03:10 AM   #4
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Quote:
Originally Posted by YashN View Post
Actually, having seen the PS Audio technical presentation by Smith, I think dabbling in proper PCM decoding could be a worthwhile pursuit, even with RedBook.
I asked him over on CA how he dealt with noise modulation which seems to be inherent in DSD (based on the Lipshitz/Vanderkooy paper from way back) and he got rather political saying he wasn't going to answer any more of my questions. So obviously there's something to hide there
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Old 18th March 2014, 03:22 AM   #5
YashN is offline YashN  Canada
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Ah, that was you! I just read that thread a few days ago. I'm not sure why he decided not to reply to you, but I remember that in the thread.

So counting PS Audio's DirectStream DAC, Putzey's Mola-Mola, the Lampizator, the Phasure and the Trinity, that's a good set of innovative and interesting DAC approaches.
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Old 18th March 2014, 03:46 PM   #6
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For myself I don't see anything particularly innovative about the PS audio latest. Reading their white paper sent the needle on my hype-o-meter wrapping itself around the end stop. I am though curious about what Berkeley Audio will come up with for their latest offering. That strikes me as one interesting device to watch...
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Old 18th March 2014, 05:26 PM   #7
YashN is offline YashN  Canada
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If I remember correctly, B. Audio is doing the opposite, i.e. converting to PCM?

For me, on the contrary, there is a lot about Ted Smith's approach which are rather innovative (not saying somebody else didn't try similar things before), but I like the FPGA approach (here again, you can say that Chord was doing that too for instance), but he seems to be meticulous in choosing and implementing his algorithms, like validating things with numerical analysis first. This whole meticulousness while hacking/optimizing appears to be throughout his implementation. There's a lot to grasp from what he did, that technical presentation video is rife with little details.

This attention to detail is very similar to Peter's Phasure and Dietmar's Trinity DAC mindset.

To come back to my initial question: let's say I get an Amanero interface. Can I tap directly into the I2S side to get the 1-bit DSD bitstream?
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Old 19th March 2014, 12:32 AM   #8
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Yes, in my understanding the BA is converting all to PCM.

There's no doubt the guys you mention are paying attention to details. The doubts in my mind are concerned with whether they're the details that matter. What I hear in listening to DSD-recorded CDs is a kind of artificial spaciousness (auditory smoke, using an analogy with film) amd HF cloudiness. As for the Phasure and the Trinity they both use the PCM1704 which brings the inherent weakness of the R2R architecture (glitchiness) to the table which neither designer seems aware of.
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Old 19th March 2014, 02:22 AM   #9
YashN is offline YashN  Canada
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It all depends on what you're looking for, isn't it? If someone has released a product with 10 innovations but you're focused on a single thing, it won't matter to you, will it?

I have more of a holistic view in the sense that I perceive the listening equipment and surrounding as a chain to be optimized. Therefore, anything helping anywhere in the chain and which adds up to a perceived effect is valuable.
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Old 19th March 2014, 02:41 AM   #10
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Sure it depends on what each person's looking for. For me, its SQ first and foremost determined not by measurements but from listening satisfaction. When people focus on the wrong things its a problem for SQ because it means they've not put enough effort into the things that really matter. Since engineering is always about optimizing the available resources, focussing on irrelevancies means money's wasted.

Most of what I see in 'high end' digital audio these days looks to me to be straining at gnats but swallowing camels. Take for example the Phasure, Peter selects for THD with his DACs but doesn't have a story (that I'm aware of) for why lowest THD (and we're talking down at the 0.001% level) matters so much. So this focus on THD means other areas get neglected as all designers only have limited attention. Ditto Bruno's work getting his DAC's THD down to immeasurable levels. He admits its a matter of pride (therefore not SQ).
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Last edited by abraxalito; 19th March 2014 at 02:44 AM.
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