I2S TDM DSD to and through UBS and S/PDIF - Page 1
Forum section: electronics / projects

author: BlackFoxTom
author_rank: Newbie
timestamp: June 01, 2018, 12:24:04 am
content: So well. I just like to think about thing I might never actually build anything or fully design it. But oh well it's simply nice to learn new things.I want to "design" ADC -> USB and S/PDIFI want to usehttps://www.akm.com/akm/en/file/datasheet/AK5538VN.pdfIt does have 32bit 768kHz I2S/TDM and DSD 256 output.Questions.Is there anything non custom made that can accept more than 32bit 192kHz I2S/TDM and send it through USB and/or S/PDIF?Is there an non custom chip that accept DSD 256(any DSD rly) and send it through USB and/or S/PDIF?

author: cat87
author_rank: Regular Contributor
timestamp: June 01, 2018, 06:46:41 am
content: Well, this is something i've come across myself recently while trying to make my own adc interface.There is no single-chip sollution for i2s to USB at anything above 192k. This seems to be the max speed interfaces or codecs top out at.Not even XMOS have anything beyond 192k for adc to usb, though they do go for 780k on the usb to dacThis being said, you can go diy and get something like a teensy 3.6 and download the audio library for it and just dump all the data drom i2s to usb directly. From some forums i've read, it can be possible to go up to 300+ k but that you'll have to actually experiment and see.Another option ishttp://www.beis.de/Elektronik/DA2USB/DA2USB.html

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 01, 2018, 11:55:34 am
content: I'm not sure what you'd like to do with 32-bit, 768 kHz audio at the moment. Even 192 kHz is considered overkill by many. A good 24-bit, 96 kHz ADC will be better than a loosy 32-bit, 768 kHz one.The AK5538, with a 103 dB 'S/(N+D)' (which I suppose is the dual of the more common THD+N) is good but by no means exceptional. So not too sure about your attraction to this sampling rate inflation.Apparently, this is the "VELVET SOUND" range of AKM ADCs. Granted digital filters benefit from higher sampling rates, but again the rated performance is not really better than other high-end ADCs from TI for instance at lower sampling rates.Anyway, back to your question. In theory, starting with the USB 2.0 audio class, sampling rates higher than 192 kHz should be supported, but I'm not 100% certain that all OSs support this fully.XMOS claims up to 384 kHz apparently?http://www.xmos.com/support/software/uac2There is a difference between hardware and software support...Yes the usual solution is not to use the USB audio class. You can stream audio with USB bulk transfers. Getting low latency with bulk transfers is a bit challenging, but doable. The end-result will still depend on the OS and the software implementation, more so than if you use the USB audio class and get guaranteed timings, so you will have to provide for sufficient buffering.As for off-the-shelf solutions, CMedia has chips that are widely used. The latest: ishttps://www.cmedia.com.tw/products/USB20_HIGH_SPEED/CM6632ADoesn't support anything above 192 kHz though. So XMOS may be your best bet at the moment, up to 384 kHz.

author: BlackFoxTom
author_rank: Newbie
timestamp: June 02, 2018, 12:18:42 pm
content: S/(N+D) is Signal to Noise + Distorsion ratio(so it's not typical SNR).About sampling rate. If belive AK data sheet sampling rate of above 300kHz get rid of other "bad" things than distorsion. Are those things hearable is different topic.(And people seem to only care about quantization noise anyway)Also arguably most accurate answer is. I simply want use this chip and find way to send all that 32bit 768kHz data ;P