Inexpensive USB2.0 Digital-to-Digital Converters (DDC) Pt.1: Douk Audio U2 PRO (Upgrade Version) and SMSL PO100 PRO - initial look, about I²S-HDMI. In praise of unofficial Atmos mixes!

This SMSL unit also does MQA decoding for those who want the feature. Unlike the Douk, this box only has an LED to indicate MQA decoding status but does not tell us the PCM or DSD samplerate.

While I've tested some inexpensive devices (like the Topping D10s DAC) which have the ability to convert USB 2.0 input into S/PDIF output, I have not specifically looked into these Digital-to-Digital Converter boxes which some audiophile reviewers (like this fellow, and this) seem to rave about.

For me, there just hasn't been any reason to be particularly interested since other than conversion from one interface type to another, the other promise of such devices - the reclocking capability - just hasn't been of great interest to me. As far as I can tell from listening, it's not like jitter has ever really been much of an issue unless severely bad for any decent modern device I've ever come across even at low price points (nor was jitter really an issue even with old CD players)!

However, since I have not tested I²S/I2S/IIS, I figure I'd buy both the Douk Audio U2 PRO 2025 upgrade version (US$63; Amazon Canada) and SMSL PO100 PRO (US$74; Amazon Canada) boxes to try out; have a listen and run some measurements. Unfortunately due to time limits, I'm not quite ready to show the measurements yet, so keep an eye out for those results, perhaps next week! For now let's just introduce you to these devices and talk about the I²S-HDMI connection.

As typical of the majority of my reviews/critiques, I bought these through retail channels.

MEASUREMENTS: JustBoom Digi S/PDIF HAT for Raspberry Pi. (Plus "Why isn’t digital audio 'just ones and zeroes'?" anxiety...)

I mentioned a few months back in September that I updated my Raspberry Pi 3 B+ Touch device with the JustBoom Digi HAT for S/PDIF coaxial and TosLink digital audio output. Over the last few months, I've been using it more regularly for my nightly music listening.

As I noted previously, this device is essentially a 1-chip solution featuring the Cirrus/Wolfson WM8804 transceiver with jitter attenuating PLL (rated intrinsic jitter of ~50ps RMS) released in 2009. It also uses the Murata DA101JC isolation transformer for the coaxial output.

The device is rather plain otherwise as you can see. It does sound good and is capable of up to 24/192 with both coaxial and TosLink outputs. And at <US$40, it's also very affordable. Let's see how well it measures!

MEASUREMENTS: Google Chromecast Audio - Part II: Digital Output

Chromecast Audio with optical TosLink adaptor & cable.

Alright, here's the follow-up to the Part I evaluation of the Chromecast Audio. Time now to have a look at the digital output using the mini-TosLink adaptor and standard TosLink digital optical out. Please refer to the previous post since I will be using the same settings and also the Plex Media Server system to run the tests today.

The first thing that needs to be addressed is whether the Chromecast Audio is capable of "bitperfect" output. Now, I do not have an easy way to capture the digital output, but one thing I can do is to make sure that a DTS signal encoded as 16/44 FLAC can be streamed from Plex to my digital receiver without audible issues... Indeed, in this regard the Chromecast succeeded.

MEASUREMENTS: Transporter TosLink vs. AES/EBU Behringer DEQ2496 Loopback.

A little while ago, I demonstrated that the TosLink loopback with the Behringer DEQ2496 in line worsened the Transporter's jitter measurements significantly here.  Although I do not believe the extra 2ns or so of jitter was audible, I wondered if using an alternate interface than TosLink would have improved the situation. Although the Behringer doesn't have a coaxial SPDIF, it does feature the AES/EBU interface which is a digital balanced cable for me to try.

So, I got a couple of  5' Mogami W3080 + Neutrik connector cables for total ~$65 shipped to take the AES/EBU interface for a spin.

Setup: Transporter --> AES/EBU --> Behringer DEQ2496 (bypass mode) --> AES/EBU --> Transporter --> shielded 6' RCA (Tributaries brand) --> E-MU 0404USB --> AMD X4 laptop (Win8)

For the TosLink condition, I'm using 2x3' generic plastic TosLink cables instead of the AES/EBU.

Firstly, I wanted to make sure the analogue output remains good/unchanged:

The upper table contains 24/88 measurements - these days, it seems more hi-res is available in 24/88 (often SACD/DSD conversions), I figured it would be good to have a look to make sure it all measured well. The lower chart are the same conditions at 24/96. Note that these are the RCA output measurements so a little lower than with the XLR results posted before. Note that there is some inter-test variability compared to my previous results with the Transporter but generally we're talking <1dB difference.

As you can see, from the analogue perspective, there isn't any difference whether I'm measuring the Transporter DAC directly, or if it's running through a total of 6' TosLink or 10' AES/EBU through the Behringer DEQ2496.

Let us turn our attention to those pesky jitters. As usual, using the Dunn J-Test:

Transporter direct (16/44):

 

Transporter-DEQ2496 AES/EBU loopback (16/44):

Transporter-DEQ2496 TosLink loopback (16/44):

At 16/44, the Transporter is very clean for both direct and AES/EBU loopback. Most of these spikes are just J-Test modulation products  from the 16-bit signal being recorded in 24-bits. As you can see, the TosLink loopback is considerably worse with more sidebands congregated around the primary 11kHz signal. You can also see that using the TosLink interface with the Transporter slightly raises the absolute noise floor in general.

The AES/EBU loopback does add a small amount of jitter to the graph but it really is quite insignificant!

In the 24-bit domain, here are the same conditions with the 24/48 J-Test:

Transporter direct (24/48):

 Transporter-DEQ2496 AES/EBU loopback (24/48):

Transporter-DEQ2496 TosLink loopback (24/48):

These graphs look a bit different from the previous Transporter jitter measurements because I'm measuring RCA output (rather than the XLR from before which has a lower noise floor). Nonetheless, the results are the same in terms of jitter - TosLink is significantly worse.

Conclusion:

Well, I think that's it for my suite of Transporter measurements... The practical side realizes that jitter at these levels even with TosLink doesn't make an iota of difference playing real music. However, the audiophile seeks for "perfection" in as much as it's possible. Using AES/EBU digital cables instead of TosLink in this loopback configuration with the Behringer DEQ2496 for room-EQ does not add any significant extra jitter within the resolution limits of my test equipment. Cool.