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I have been looking at USB to SPDIF converters recently and understand that there is a lot to choose between. From the reviews, it seems that there IS a difference in the sound quality - partially subjective but also partly measurable.

Does anyone know the main source/s of degradation in such products?

In my case, my DAC cards use a good DAC (PCM1792) and a dejitter function (Si5317) - so I am left wondering what is the added value of a top quality USB-SPDIF converter (I may have taken care of the issues that make such a converter 'top quality'). By the way, the transmission is via optical cable.
It might be placebo (as pretty much everything in this business lol), but IMHO you need clean power to the clocks. I have a modified Hiface with 3.3v going from the rechargeable batteries and I think I can tell the difference. At least in theory it can matter. Also you need asynch.
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In most DACs and digital receivers, the first thing the clock sees is a jitter cleaner, so in 99.99 % of cases you will get absolutely nothing out of providing an ultra-clean clock. Note that the way jitter cleaners work is that they replace the incoming clock jitter with their own PLL/VCO jitter profile within the band of interest. Note that at offset frequencies below the PLL loop bandwidth of the first stage in the jitter cleaner, you will have some reference clock noise come through. The PLL loop bandwidth of the jitter cleaner can be made ultra-low by using a DPLL, so basically clock noise is an issue that's been dealt with already and there isn't a lot of science to back up any perceived differences between an ultra-clean audio clock and a regular audio clock. Not a lot of engineering science anyway. There's plenty of psychological science around expectations, cognitive biases, etc. that can explain why some hear a difference. :)

I brought up cheap vs expensive optical cable in the week wondering why the huge price fluctuations vs sound quality if there is virtually no difference in SQ to offer, "they either work or they don't". Fair enough, I buy that.

But I will be passing the cheapo $10 links over to my nephew to use on his less sensitive electronic devices. I wont experiment with those anymore. Every so often in the split of a second while advancing channels I get a random what sounds like a heavily amplified static electricity discharge through the L or R upper frequency. That was enough to convince me not to mess with them.
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What USB --> S/PDIF converter do you use?

So are some USB to S/PDIF Converters better than others?

I want to feed the input of my nanoDIGI DSP, using windows laptop for now, streaming HiRes from Tidal mostly, but sometimes Apple-Lossless for iTunes.

I can input my DSP with optical or coax, but my computer only has USB 2.0

The converters that have caught my eye are:
1. Peachtree Audio X1 Asynchronous 24/192 USB to SPDIF Converter $150

2. iFi micro iLink $265

3. Gustard U12 32Bit / 384KHz DSD XMOS USB Digital Audio Interface $170

Anyone have experience with any of these?
Other options in this price range I should consider?
Should I just find a $30 converter instead?

I use one of the CM6631a-based boards available for little money from lots of places. Confirmed on scope, it delivers a 384k/24 readable output in spdif format with 384k input. If I only had something that would read and downsample that, I could run some tests. Anyway, these things work very well at any sample rate, and have coax and optical. I'd probably try a USBstreamer except that for my purposes coax output is desirable, and I have a ministreamer (in use elsewhere), but it tops out at 96k.
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Well, I was part of that test, remember? The HiFace convertor did just fine, but no better than your happy Chinese convertor. However, I did find a few cheap ones that I had bought off eBay that were not so happy. CMedia chips, of course.
It's hard to decide on a USB S/PDIF Converter.

My DACs are 3 matching Little Bear 24B/96K. They sound great and were very inexpensive. Yet the no name DAC I got for $20 is noisy and I think it doesn't output enough gain or something,.. Don't know how to describe it but I don't like it.

I believe that some spdif converters in the sub $200 range can compete with some in the $600 range, yet still there are a few in the $30 range that sound as good as the $200 ones. Is my belief flawed or delusional? Do they all sound the same?

For now I decided I'll just think on it longer. I'm building some subwoofer cabs now instead. I'm streaming through wifi, but it caps at 16/48 in think; in the future I'll want to use USB capable of 24/96.
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