MQA Hi Res Audio – Streamings Holy Grail
Introduction
There are now enough articles, streaming services and CD’s that I thought that I would re-visit MQA encoding, particularly after several e-mail exchanges with David Elias, a Hawaii based Acoustic Music writer, producer and studio owner. David writes, produces and records mostly acoustic folk material and was an early pioneer of SACD. After his introduction to MQA over a year ago, many of his older albums and his new albums are now being released encoded to MQA. David provided a selection of both stereo and multichannel SACD and stereo MQA files to OPPO, which can be downloaded for free from their web site here.
MQA Recap
This is NOT going to be a detailed technical explanation of the process. Why? Most potential users want to know is it worth having, if so, what do I need to play it back, and, if I do this upgrade is it worthwhile? So, while I am an engineer, I do not want to burden my readers with technical details that are really not that important and to many are really boring. For those looking for more technical information please see the links at the end of this post.
For those new to MQA, what is it? Why do we need it? How does it work? What do I need to play MQA? Can you hear the difference?
Let’s look at these questions one at a time.
What is it?
MQA – The Technology
MQA stands for Master Quality Authenticated– this audio technology was developed by Bob Stuart, co-founder of Meridian Audio and is the CODEC (coder/decoder) that makes high resolution streaming now a reality.
MQA claims that its processed track data uses very similar bandwidths to those used by streaming standard CD tracks. So if you can stream CD tracks, you will most probably be able to stream MQA encoded tracks. This means hi-res audio streaming is now possible, with songs being delivered to the listener almost exactly how they were recorded in the studio, without requiring huge amounts of bandwidth.
Remember that MQA IS NOT LOSSLESS. It is just not very lossy. It uses some very clever signal processing techniques to squeeze a higher quality signal into a lower streaming bit rate.
This is not a new file type that adds to the myriad of existing wrappers like FLAC and ALAC. MQA files are packaged inside any lossless container such as FLAC, WAV or even ALAC. To decode the almost lossless versions of this file you will need compatible hardware and software or a desktop app from the streaming service.
This development has already managed to get many hardware manufactures on board to support it and the list just keeps on growing.
Some existing items of hardware can be upgraded with just software to support at least part of this new standard. However, all CD players can play the most basic ‘CD quality data layer’ of this format.
Why do we need it?
I’ll make this as short and simple as I can. Early CD’s sampled the analog signal at 44.1KHz and to prevent some horrible distortions the recorded and played back signals needed to be severely filtered (see Nyquist-Shanon) by what is known as a Brick Wall filter that stops anything above 20KHz being processed or replayed.
Typical 20KHz Brick Wall Low Pass Filter
These filters produce an effect called ringing. It’s a bit like every transient becoming a hammer and hitting a bell. This in turn results in an effect called temporal (time) smear where the impulse shows additional energy before and after it during a time window of about 4mS. The effect is often referred to as pre and post ringing and it is not observed in natural/live sounds. It can clearly be seen in the Oppo 205 filter impulse response shown below for a sample rate of 44.1KHz.
As the human ear can resolve timing errors of less than 10 micro seconds it is not unreasonable to assume it can hear these effects, being well within the time window for this temporal blurring.
Predicted temporal blurring for MQA and conventional encoding sample rates.
24/192 Linear Phase & MQA Temporal Smear
This temporal blurring is audible and is said to give CD’s their characteristic digital sound. The problem can be reduced, but never eliminated, by increasing the sampling rate. This makes for a more ‘gentle’ filter and reduces the temporal smear which is a major contributor to this digital sound and its potential impact on the openness and imaging of the music. However, as can be seen from the above graph, even at a 192K sample rate, a linear system end to end temporal smear is still much greater than that of an MQA encoded signal.
This is primarily what MQA claims gives it its superior audio performance.
How does it work?
In simple terms this new file format is a bit like a Matryoshka or Russian Nesting Doll. The file data structure is composed of three layers, which could be considered to be folded in on each other with bit depths between 13 and 24. The bits beyond 17 are used to carry the additional data used to create what is a virtually lossless signal, provided that the data in the ‘touch up’ channel never overloads. The resulting file can be carried by any lossless wrapper like FLAC.
Layer 1 -lossy
No MQA or an Authenticated decoder -Equivalent (or better) audio quality to a CD, with a sample rate of 44.1KHz or 48KHz and a bit depth up to 16. This file can be played back by any conventional DAC.
Layer 2 – almost lossless
MQA core decoder -Equivalent to playback at 88.2KHz or 96KHz with a bit depth of up to 24.
Layer 3 – virtually lossless
Full MQA Decoder with stream authentication unfolds the last layer of data and manages the DACs performance to provide the highest audio quality possible that this technique can support. This supports full Studio audio encoding at up 768KHz at 24 bits.
So, depending upon the performance of your hardware and software you can access the base layer 1 for CD quality, layer 1 and 2 for high resolution almost lossless audio, or layers 1, 2 and 3 which provides you with audio quality approaching that heard from the original master tapes or source. The decoding is a transparent process to the user, as the playback hardware and software recognizes which layers it can handle and adjusts the playback quality automatically.
Depending upon the musics original MQA encoding, your streaming application, firmware and hardware, the MQA encoded bit stream can be decoded to various bit levels and rates to include:
Original MQA file encoded at 24/192:
- Layer 1 – No MQA decoding <16(24)/48
- Layer 2 – Software decoding 24/96
- Layer 3 – Hardware decoding 24/192
Original MQA file encoded at 24/176.4
- Layer 1 – No MQA decoding <16(24)/44.1
- Layer 2 – Software decoding 24/88.2
- Layer 3 – Hardware decoding 24/176.4
Original MQA file encoded at 24/352.8
- Layer 1 – No MQA decoding <16(24)/44.1
- Layer 2 – Software decoding 24/88.2
- Layer 3 – Hardware decoding 24/352.8
What do you need to play MQA?
MQA is typically encoded within a FLAC wrapper. This allows ANY CD/DVD player to play an MQA encoded CD base layer just like any CD with a similar quality. If you are looking for the improved audio performance that MQA offers you will need either a software decoder that can unwrap level 2 or a DAC that can unwrap and fully authenticate layer 3.
Many streaming applications and a growing number of Blu ray and CD players are offering at least level 2 software decoding. Level 3 or Studio decoding requires the software to communicate with the DAC in order to optimize the final layer 3 unwrapping. This requires software and a DAC that is specifically designed to execute this function, with the connectivity often being over USB; hence the term USBDAC.
Rather than listing the significant number of devices that can now support MQA, I leave it to the reader to review their requirements with vendors.
As of 9/2/2018 the only UHD Blu-ray player that can fully support MQA decoding is the discontinued Oppo 205. This player fully supports all levels of decoding for MQA file streaming, CD playback and USBDAC input. There are several CD players, a number of personnel players, network streamers and many USBDACS that can be used to decode the USB output of streaming applications like Tidal and Roon. Please click the following link to see a current list of manufacturers who support MQA.
Can you hear the difference?
Yes….much to my surprise! Fully decoded to level 3 it sounded very good, and similar to many of my SACD’s, but does NOT exceed the performance of many of my Direct To Disc vinyl recordings.
The quality is the closest that I have ever heard from a “low bit rate” CD format that reminds me of being back in the studio. It exhibits little of the digital hardness and is a very open sound with good imaging and depth. Vocals and instruments took on a more open and natural sound and it gives the recording acoustics a more open feel.
All these comments are of course predicated on the original masters being well produced in the first place, unless this is a new encoding created from a live recording session. READ ON!!
My Experiences With MQA
So, after installing my Oppo 205 I decided that it was time to test out its support for MQA. This player supports playback of MQA encoded CD’s, FLAC/MQA streaming and an MQA USBDAC. The latter requiring a firmware upgrade to fully support the required authentication and final unfolding process.
I need to point out here that I do not subscribe to any streaming services so my first tests used a USB stick to which I loaded the files. This worked most of the time, but I found that some of the files were corrupted causing them to be truncated or to generate bursts of noise. However, once I installed Twonky, a DLNA media server on my Mac Pro, streaming FLAC/MQA and DSD/DSF files was flawless except for a couple of DSD tracks that were corrupted causing occasional bursts of noise. Selecting and controlling tracks using with the Oppo iPad application was child’s play, even if a little basic.
Material used for the listening tests were:
- Rebecca Pigeon – The Raven – CD – 24bit/176.4KHz
- David Elias – The Window & Crossing – Files – 24bit/352.8KHz
- A selection of classical recordings, MQA and DSD, from the links on the Oppo web site – Files (various)
- Various selections from Tidal – Being a golden oldie who streams nothing, it took me a while to find my way around the application, install and setup the desktop player to drive my MQA USBDAC and find the MQA encoded material; sending it out over my temporary Windows Laptop USB connection. I was not impressed with the selection of MQA material, it was difficult to navigate and none appeared to be encoded above 192KHz. Some tracks were MQA encoded as low as 48KHz!
Methods of Playback for MQA material:
- USB thumb drive
- CD
- Streaming off my Twonky media server
- Tidal streaming via their desktop application over USB. Set to Master, Exclusive Mode and MQA Passthrough.
Methods of connectivity from the Oppo 205 to my Denon AVP A1 for MQA playback:
- Analog stereo – balanced. Full unfolding to Studio 24bit 352.8KHz or 24bit 176.4KHz (level 3)
- HDMI – NOTE: this limited my MQA unfolding to 24bit 88.2/96Khz. (level 2)
Methods of connectivity from the Oppo 203 to my Denon AVP A1 for the MQA CD base layer playback:
- Analog stereo – unbalanced <16 bit 44.1KHz (level 1) NOTE: The AVP uses exactly the same analog path for balanced and unbalanced analog audio inputs.
- HDMI – <16 bit 44.1KHz (level 1)
- The default playback filter for these listening tests was Short Delay Sharp. (I could not detect any significant audible differences between any of the filters.)
NOTE: The Oppo 205 will always unfold MQA to the highest level that can be supported by the audio connection in use. In my case levels 2 and 3. Even the Toslink (SPDIF) connection registered an 88.2KHz stream.
Listening Observations
MQA Playback (Layers 2 and 3)
The only issue that I found confusing was that the bass from the 24/352.8 Studio quality analog signal for The Window and Crossing albums had more “body” when compared to the 24/88.2 HDMI digital audio. I cannot account for this as it is not the case when I play SACD’s or CD’s via the 205 analog output. It may be that I was hearing what actually got recorded, and that the HDMI digital version is processed in some way making it sound “cleaner and tighter” (more sterile?). This was not a distraction nor criticism of the excellent sound of these albums, just a noted difference in my system.
As to all other aspects of the sound there were some notable improvements, all audible over both analog and digital HDMI connections. What I did find surprising was that the differences between the digital 88.2K and analog 352.8K signals were not earth shattering! This could be that the 1038 Genelec’s are not exactly renowned for their refined analytical performance and/or at my age my ears are just not cutting it any more, or both!
Despite the above comments the audio was notably improved over a standard Red Book CD. Unfortunately I have no way of comparing the MQA encoded material against the original studio performance or LPCM CD version of the SAME master recording. The Window, Crossing and other recordings by David Elias had no digital hard edges, the imaging was open and pin point, with good depth placement. Instruments took on an enhanced degree of realism and openness with vocals sounding very natural with no hints of sibilance or mid-range hardness but lots of precence. Nor was there any obvious compression.
Comparing a number of David Elias MQA files to their SACD versions, the differences were subtle, whether over analog or digital connections. My initial impressions were that the SACD versions seemed to be a little brighter and more dynamic, but the vocals were a little more sibilant and edgy, particularly over digital. To be honest, I actually preferred the MQA encoding due to the more natural and smoother vocals.
The Classical MQA encoded files dowloaded from 2L also sounded very open with excellent spatial positioning. However, Rebecca Pigeons CD didn’t sound significantly better than some of my better Red Book CD’s and was definitely not up to the performance of most of my Hi-Res DVDA’s and SACD’s. The instruments and spatial positioning were very good but the vocals sounded a little hard and edgy and the dynamic range seemed restricted.
The Window, Crossing and many of the files by Davis Elias, provided a significant improvement over a 44.1 LPCM CD, being very similar to SACD, transporting me back to my days in the studio control room. I cannot say the same for The Raven by Rebecca Pigeon.
For Hi-Res streaming (24/192KHz) this encoding technique provided some marginal improvements over conventional streamed 44.1KHz 16 bit FLAC. Not enough to my ears to want to subscribe to a service. I was NOT wowed!! However, for little increase in streaming bandwidth it did provide some audible benefits, none of which rose to the level from either of the David Elias album files.
CD Playback (Layer 1)
The Raven provided no audible improvements over many of my Red Book CD’s, either over analog or HDMI connections.
It is quite possible that some of the MQA improvements I heard, particularly with the David Elias material, are a result of his attention to detail during the recording process. This I suspect is particularly true for his material as he has been a pioneer, burning the path and a leading the way, in both DSD and MQA encoding for years.
Remember MQA encoding is NOT some magic panacea that makes recordings sound great. For re-encoded material if it wasn’t there in the first place MQA will not put it back. What it should do is to remove all the unfortunate side effects of PCM and its filters so that you can hear a closer representation of what actually got recorded in the studio.
As to any audible benefits of using MQA encoding over SACD or uncompressed 24bit 192K LPCM for the production of plastic (CD’s), I am not convinced yet.
The format did not equal the performance of many of my vinyl Direct Cuts. There again, neither do many SACD’s or Hi-Res discs! However, some of David Elias’s tracks came very close.
It would be worthwhile for any prospective audiophile who intends to enter the world of MQA to read the following independent disc Reviews and Forum:
Marketing & Buisness Issues
MQA is an end to end proprietary solution. In which many aspects of the recording and playback process are under the control of MQA tools and licensing. Which will ultimately probably create a very profitable financial stream. My concern is that as long as it is just MQA and Bob Stuart running the show, all will be well, and provides the consumer with worthwhile and tangible benefits. However, it is only a small leap to see how this lock on technology and work flow, could be purchased by large, not so naive, record labels, and used to squeeze the consumer. Business partners, shareholders and financial houses who are part of this development are not naive, they are there to turn a profit. I have been on the receiving end of this big stick several times in my career and it never worked out well, at least not for me!
For MQA albums that demonstrate the performance of this new format, click on any of the following links:
- David Elias – Independent Acoustic Music
- Oppo Digital – Free Hi-Res samples – MQA and SACD
- CDJapan – Universal Music Japan
- Tidal – Streaming
- 2L The Nordic Sound – Free file samples. A great resource to compare many encoding formats.
For more detailed technical information regarding MQA please click on any of the following links:
- MQA Home
- Bob Stuart Talks
- Stereophile
- ARS Technica
- Audiostream
- MQA Technology – Sound On Sound
- Darko Audio
- The Absolute Sound – MQA Series
