Hey folks... It's summer and I'm in and out of town doing a bit of R&R mixed with the day job.
I sent my friend with the Mytek Brooklyn and Fireface ADC a package of the MQA "Render" tagged files for testing. As you can see above, that's what the MQA filters look like with the Mytek Brooklyn serving as "Renderer" for the impulse responses. If you look at the top row, we see that the Brooklyn's standard digital filter at 24/96 is the same as what MQA uses for playing back 96kHz "original" unfolded PCM. This is different from the Dragonfly Black DAC presented a couple weeks back where the standard filter at 24/96 is a much sharper one and would shift to the weaker MQA filter only when it detects the MQA Render tagged data.
Here's the previously published Dragonfly Black table of impulses equivalent to the Brooklyn for comparison:
As you can see, the impulse responses are very similar. Slight differences may be attributed to the ADC used to capture them to some extent - Focusrite Forte vs. RME Fireface; both at 24/192. The overall morphology suggests very similar parameters being fed to the ESS Sabre DAC's programmable FIR filter used in both the Dragonfly and Brooklyn (as expected). We know the Meridian Explorer 2 uses the TI PCM5102 DAC chip but unfortunately that DAC does not respond to these MQA Render flags. It would be interesting to compare the consistency of the filters across DACs especially for those not based on the ESS chips when we see more Renderers released.
One very consistent impulse response is that which is used for MQA 96kHz rendering:
If there is one "typical" impulse response for MQA, it would be this one. Even though the Meridian Explorer 2 does not respond to the Render parameters in the stream, when sending 24/96 data to the DAC, it already uses that digital filter. As such, we can say that MQA Core expects the DAC to play back the unfolded data using that kind of digital filter setting for 96kHz "original" recordings.
A few months ago, I took a stab at MQA filter emulation using iZotope RX. Well, now that I've got these impulses for confirmation on the filter design, the actual filter is even less steep than I thought! Here are the parameters for "pseudo-MQA" for 96kHz playback:
So, with that, what one could do is rip the 24/96 digital output from an MQA Core decoder (TIDAL or Audirvana) for a song that is originally at 24/96. Then use iZotope RX with those settings to upsample to 24/192kHz. This final file would include the effect of the MQA-like digital upsampling filter (eg. the poor antialiasing performance and whatever time-domain benefit they might want to claim).
You can then take that 24/192 file and play it back with any reasonably accurate / high quality DAC and get a sense of what MQA would sound like with an actual MQA Rendering DAC like the Dragonfly. If you give this a try, let me know what you think! A good example on TIDAL of 24/96 "original" MQA-encoded music would include stuff like the Led Zeppelin "Masters" which I know is the same mastering as what HDtracks sells.
For those a little technically inclined, you'll know that doing what I'm describing above would not be difficult at all. In fact, I wish MQA could have just taken a few moments and provided a few post-processed files in 24/192 so consumers could hear the difference between "original" Studio Master compared with "de-blurred" MQA output with all the processing including the effect of the upsampling filters. There would actually be no need for A/B comparisons at audio shows since everyone would then be able to figure out if MQA provides any benefit for themselves at home. Let's not be naïve though, of course MQA would not want to do something so simple; this would only burst the bubble of the implied mystique they're apparently after with all the secrecy and hyped-up claims of sonic improvement...
To close, I was wondering if anyone can show me a single example of where a simple, direct generic USB2.0 cable between a computer / Pi / streamer to a USB DAC actually results in compromised analogue output from the DAC.
The reason I ask is because over the last few years, there has been a proliferation of devices that supposedly clean up the USB interface by doing all kinds of things like "filtering" noise, "regenerating" the data signal with an improved clock to improve jitter (as if this is beneficial with modern asynchronous USB DACs), "isolation" apparently also removing noise in the data lines, "injecting power" with cleaner power supplies, and maybe other stuff not mentioned.
Remarkably, some of these devices even claim that with the device in place, it often "sounds like you are listening to a different DAC"! Really? Like I said, it would be nice to demonstrate just one example where there is objective evidence of such an effect with a description of the computer / streamer and DAC used. It should not be hard to show the difference especially since it could sound like a "different DAC", and differences of this magnitude would be easy to show. (As usual, subjective opinions are easy to find, especially for the faithful early adopters willing to put $$$ down.) Remember that a year ago, I discussed that even with different USB devices like the i5 NUC, ODROID-C2, laptops, or full HTPC computers, they made no difference to the DAC output. One could later add the Raspberry Pi 3 to the list.
Even more remarkable is how some people appear to be so convinced by these claims that they would even stack multiple of these devices together! For example, this reviewer admits that there are 9 devices in his playback chain to deliver the audio files between server to DAC with ethernet and optical cables in between. Some of it might be reasonable but surely it seems unreasonable to suggest all nine of these devices would be able to additively or synergistically improve the sound, right?
From my perspective, it's much more likely that one is simply wasting money without cause based on a placebo effect or simply faith in manufacturer claims. But even worse, there is the likelihood that all those devices may worsen sound quality by creating potential data error with all that extraneous reclocking / filtering / isolating going on! Would you ever consider it a good idea to hook up your USB hard drive with important data on it to the computer in this same fashion without some hesitation around data integrity or check if transfer speed may have slowed down? Does anyone really think that reputable DAC engineers these days are so incompetent as to create DACs with such horrible noise, jitter, and susceptibility to power irregularities as to require a number of third-party add-ons like this?
It has been at least 2 years now since such devices like the AudioQuest Jitterbug and Uptone USB Regen have been released. More recently we see stuff like the iFi iPurifier. Some of these like the SOtM tX-USBUltra cost more than very good DACs. In all this time, I have not seen any measurements to confirm significant benefit to audio playback from any DAC. At best, they've used USB eye patterns to somehow imply audibility (and act as if very expensive USB signal analyzers somehow are necessary for justifying the sonic voodoo being peddled). This is just as meaningless as HiFi News and their USB cable test years ago. I've even seen some folks stick these USB devices in front of S/PDIF / AES/EBU / HDMI-I2S converters like the Singxer SU-1 as if this is able to achieve anything good by the time the signal reaches the DAC!
No thanks. Personally, I just don't find this stuff "cool" nor a wise use of dollars that could be directed towards purchasing a better DAC if needed and good music among many other beneficial acquisitions and experiences. They seem to be nothing more than a psychological salve for those with unfounded insecurities (typical of those who also have a strong faith in things like expensive cabling).
Okay, back to the summer schedule :-). Just had a great time in Arizona, Nevada, and Utah enjoying the Grand Canyon and Zion National Park with the family over the 4th of July.
Hope you're all enjoying this time of the years... And of course enjoying the music while doing so!