I2S driver for the DS


#1

Dear Ted,

Would you be so kind to explain how the I2S signal works between emitter and receiver, just enough so that I understand the need of a driver?

I thought I2S was crude and passive so only a generic way of using it existed…

I’m currently trying Volumio on a Odroid C2 board by Hardkernel. Hardkernel has a driver for an I2S DAC they provide and when I connect the DS I get PCM and DSD64 fine but DSD128 is all scrambled and recognized as PCM 16x352.8 by the DS.

The board is capable of PCM 32x384 so I hoped DSD128 would be achievable…

Do you know about the insides of these drivers and what I could change to have a signal better recognized by the DS?

I’m trying to get details from Hardkernel as well and will let you know when they provide any information…

Thanks in advance!

Charles


#2

Tho I don’t think you are confused about this I still want to clarify: we are talking about an electrical hardware driver not a software driver like those for various hardware units in a PC…

When a signal needs to go farther than a few inches, or thru some connectors to another box in general it needs more current and possibly more sophisticated transmitters and receivers than it would need for a simple chip to chip connection on a single PC board.

To lower noise we use balanced drivers and receivers for the I2S connection over a HDMI cable which is designed to support four balanced connections (among other things.)

At the hardware level we use LVDS voltage and current levels for the I2S connections, tho the receivers should support wider differential voltage levels.

Still I don’t think this is where your problem lies: if the DS is only reporting 16 bits for double rate DSD, then it’s either receiving only 16 bits or the bottom bits of the signal are always 0. Either way it’s probably not a hardware problem. It’s much more likely to be a software problem or configuration issue in the software that’s not properly wrapping DSD into DoP for some reason at that frequency.


#3

Ted, this is somewhat of tangential question … with the DS what is the maximum recommended length of cable for I2S? Does cable quality effect that maximum length? Thanks!


#4

The maximum length question is very hard to answer - it depends on the quality of the HDMI cable and (perhaps ironically) some of the “audiophile” HDMI cables probably have to be shorter since they, on average, seem to ignore more of the specs of HDMI, USB, etc. I wouldn’t be worried about HDMI cables that meet spec or are shorter than, say, 5’? I wouldn’t count on a 10 or 20’ HDMI cable, but it won’t hurt anything to try a longer cable. Just make sure the bit perfect test works reliably.


#5

Thanks Ted! I have an NPC which is connected to the DS via I2S. I was using a 1M cable but had to move the NPC and the 3M PS Audio Cable I bought for that purpose wasn’t long enough. The only other cable I had was a 20’ Blue Jeans bonded pair HDMI cable which seemed to work, but I want to get a more permanent solution. If I can position the NPC to make the 3M work then I should be fine, otherwise I’ll get another Blue Jeans cable made to the shortest length. The NPC is currently at PS Audio so can’t do much with the cables at this time.


#6
Ted Smith said The maximum length question is very hard to answer - it depends on the quality of the HDMI cable and (perhaps ironically) some of the "audiophile" HDMI cables probably have to be shorter since they, on average, seem to ignore more of the specs of HDMI, USB, etc. I wouldn't be worried about HDMI cables that meet spec or are shorter than, say, 5'? I wouldn't count on a 10 or 20' HDMI cable, but it won't hurt anything to try a longer cable. Just make sure the bit perfect test works reliably.
Hi Ted. I don't recall - do we have the ability to play the bitperfect track from a burned CD-ROM? I'm getting ready for the new transport and I got a 2m Nordost Silver Screen. I want to use the PWT now to make sure the cable can pass data properly.

#7

The bit perfect test files are normal 24/96 and 24/192 FLAC files. Depending on your transport you may want to convert them to WAV before burning them to CD-ROM (Sorry I don’t specifically know about the PWT.)


#8

Thanks for the answer Ted, I agree it’s certainly not a physical problem.

The wire used to connect the I2S pins from the C2 board to the LVDS module is 3" long, and my hdmi cable is 3’ long. I could try with a 1.5’ that I have as well by moving my “lab”…

here’s a picture of the LVDS module made by Audio-Gd and custom cable for the Odroid C2

Hardkernel answered that above 192khz the I2S output format switches from 128fs to 256fs, do you know what that means for the DS?


#9
Ted Smith said The bit perfect test files are normal 24/96 and 24/192 FLAC files. Depending on your transport you may want to convert them to WAV before burning them to CD-ROM (Sorry I don't specifically know about the PWT.)
On the PWT it is necessary to burn them as a WAV file.smile

#10

Thanks Ted and Paul. Now I just need to remember where I have them stored on my music server!smile


#11
Linvincible said Hardkernel answered that above 192khz the I2S output format switches from 128fs to 256fs, do you know what that means for the DS?
256fs is only fast enough for 16 bits (44.1k*256 / 352.8k) = 32 bits / stereo pair of samples = 16 bits / sample) It needs to go to at least 384fs (16.9344MHz) to get 24 bits / sample.

#12

Thanks Ted,

their specs webpage say it supports 384khz but I suppose it’s with short words then.

Another dead end…

hey everyone I have a PCM + DSD64 platform with I2S hdmi output for sale ;o)