AMB Laboratories DIY Audio

[judderod]

Well the seller of the SPDIF finally got back to me with the typical Chinese seller response - completely ignoring the question and offering a different response

Thanks for the advice linux-works. So it looks like there aren't really any good SPDIF-I2S solutions available at the moment. I'll have to part-build and use a γ1 sometime along with the γ2 in the future when I can take the time the learn how it all works.

It's a shame the USB section of the γ1 doesn't support the native 24/96KHz input format of the γ2...

[linux-works]

the y2 can do 24/192 I believe (so can the y1 via spdif! I've seen 192k come thru on mine, even over opto). both dacs and spdif receivers work up to 192k. only the usb bridge part stops at 48k (I'm sure you knew that but I wanted that to be clear; the y1 is functional at 192k but just not via its own local usb port).

but all of the standard driverless usb sound cards stop at 48k. to go beyond that means you are in the brand new (very new) class-2 usb audio or you are proprietary (like EMU or even firewire like RME).

boxes and chipsets that can do usb/spdif audio at 192k are in a class range well above the y2 pricepoint, just as the usb part (a whole Soc, system-on-a-chip), alone.

[amb]

It's a little more complicated than that. The γ1's coax and optical input receiving circuitry can work up to 24/192. When mated to a γ2 with the SRC4192 ASRC chip installed, 24/192 audio will indeed play through γ2's analog outputs (albeit downsampled to 24/96). The γ1's WM8501 DAC chip is configured to support only up to 24/96 (it gets a 256fs master clock for better digital filter response). So, if you give it a 24/192 stream, it will not output anything at its analog output.

Of course, through the USB input the maximum is 16/48 due to the reasons linux-works mentioned above. In fact when the γ1 was designed, there was no DIY-friendly solution for high-res USB audio.

[judderod]

While we're one the topic of inputs and sample rates, I wanted to ask if these different sampling and resampling rates can be set differently.

98% of my audio is currently 44.1KHz 16bit, CDDA standard. I could understand that upsampling to any multiple of 44.1KHz, say up to 176.4KHz could prove beneficial, but upsamling to 96KHz or some other fractional multiple must mean that some interpolation takes place. That can't be good as some samples will have been calculated, rather than simply reproduced.

[amb]

Simple "upsampling" is not beneficial on its own. It doesn't create any new information that isn't already there.

The purpose of the use of ASRC (asynchronous sample rate conversion) in the γ2 and many other highly regarded DACs such as the Benchmark DAC1, is not for sample rate conversion per se (even though that's what the end result is). The main benefit of ASRC is jitter elimination. How this works is much more than what I could describe here, but I encourage you to read this thread at diyaudio.com:

Asynchronous Sample Rate Conversion

The secondary benefit of upsampling is that the DAC will now be operating at the higher sampling rate, which moves the action of its anti-alias filters well above the audio band, reducing its ill effects within the band.

[judderod]

I've had a read... Interesting stuff.

So from what I understand, the original signal is re-clocked to a much higher sample rate than the desired output. The missing values are interpolated. The output clock runs async, and when a sample is required, it is pulled from the most recently occuring value from the re-clocked and interpolated input?

It does sound like that will work well.

[wata]

there's a very hot new 'usb dac' that gives i2s output and a pair of analog outs. you have to hack the i2s but its easy (I'm about to do it, myself, and I'll report back how well it went). best part is that its standards based, does not need drivers (except windows, lol! isn't THAT a switch!) and goes up to 192k/32bits over usb asynch (audio class 2 stuff). you do NEED a computer since its usb based and so you'd lose spdif inputs. but if you want 'something with i2s output' this might be an option:

http://www.diyaudio.com/forums/digital- ... idget.html

Indeed very interesting project, I have been looking for while now for usb 2 i2s or usb 2 s/pdif 24/192. I know there a few solution but none of them support linux. This works out the box with linux UAC2. Can one take this design and create (open source), let say USB ---> SRC4192 --> dual mono WM8741 or PCM1794 --> discrete output stage ?. Using asynchronous USB is there are need for ASRC?

[amb]

Indeed very interesting project, I have been looking for while now for usb 2 i2s or usb 2 s/pdif 24/192. I know there a few solution but none of them support linux. This works out the box with linux UAC2. Can one take this design and create (open source), let say USB ---> SRC4192 --> dual mono WM8741 or PCM1794 --> discrete output stage ?. Using asynchronous USB is there are need for ASRC?

What you describe is very similar to a portion of the upcoming γ3.
I will start a discussion thread on that soon, when I find the time.

[wata]

I knew it !!!, cant wait. This is very exciting.

[judderod]

I too look forward to hearing more about the upcoming γ3.

Just one question... Is there any chance it will be able to decode and output multichannel (>2) audio?