At CES 2017 Tidal announced it was streaming MQA masters and MQA Ltd announced software decoding of the MQA signal. Two big items for all of us who enjoy music. Immediately the questions and conjecture started flowing. It's human nature. We ask questions and make guesses about what's happening, when we don't have all the information.
Shortly after the announcements I setup a meeting with MQA's Bob Stuart to get more details about decoding MQA signals. I wanted to know the differences between software and hardware decoding and where rendering comes into play, in addition to many other items.
A PhD isn't required to enjoy MQA. This article is my attempt at explaining how decoding and rendering work, from a civilian perspective. Most of us have seen the music origami graphs and deep technical explanations, but have no idea what any of the information actually means for us, enjoying music at home or on the go. I want to help members of the CA community understand how to get the best sound quality out of MQA.
From The Distribution File Forward
Currently MQA music is offered through online stores for purchase and download, and through Tidal for streaming. I'm willing to bet more music will be available through both channels and both channels will have more outlets in the coming months.
Consumers purchasing or streaming MQA music will see either 24 bit / 44.1 kHz or 24 bit / 48 kHz files without playing the audio (16 bit MQA files are outside the scope of this discussion). These are what's called the distribution files. They have been through the MQA process that deblurs and folds them into a smaller package, readying them for transport and playback on almost any device.
The MQA distribution file, the file that's actually purchased or streamed, is like a chameleon. In its packaged state the files are 44.1 or 48 kHz, but decoded and rendered the files can expand into the highest supported sample rate of the digital to analog converter inside the DAC..
Real world example:
1. The studio creates a track at 24 bit / 352.8 kHz DXD.
2. The studio uses the MQA process on the track, packaging it as 24 bit / 44.1 kHz.
3. The consumer purchases or streams the 24 bit / 44.1 kHz track.
4. The consumer's playback system decodes and renders the track at 24 bit / 352.8 kHz DXD.
Squeezing The Best Quality From MQA Music
With the aforementioned real world example in mind, let's look at how to play MQA music and how to get the best sound quality possible. There are four "ways" to play MQA music. I use the word "ways" for lack of a better, more specific term.
A. No decoder
B. Software / Core Decoding
C. Software / Core Decoding with Hardware Rendering
D. Hardware Full Decoding
Similar to a dual layer SACD that plays the CD layer in a standard CD player and the Super Audio layer in an SACD player, MQA music is playable through almost any playback system, but the highest quality is only possible with the appropriate solution.
Playing MQA on a system without a decoder, will enable the consumer to hear the 24 bit / 44.1 kHz (or 24 bit / 48 kHz) version of the music in the example above. According to MQA Ltd, playing the un-decoded version still enables the consumer to benefit from the deblurring processes used in the creation or folding of the track.
Examples of systems without decoders are plentiful in this early phase of record labels rolling out MQA music. JRiver Media Center, Amarra, HQPlayer and many others are applications that don't decode MQA. In addition, most hardware on Earth doesn't decode MQA at this time.
One scenario that may confuse consumers, is when an MQA renderer is present without a software or hardware decoder. This will result in an un-decoded signal exactly as it would without the MQA renderer. The 44.1 or 48 kHz version of the file will play, undecoded. One example of this is the upcoming AudioQuest DragonFly (updated Red and Black versions). Without a decoder in the playback chain, an MQA renderer has no effect on the audio.
Software / Core Decoding
MQA is a whole host of processes and technologies, but for purposes of this civilian discussion, let's look at it as three processes. MQA files can be 1. Fully decoded, 2. Software / core decoded, and 3. Rendered. Software decoding is capable of exactly what its name suggests, decoding MQA. Rendering must be done in hardware because it is custom matched to the DAC system.
Software decoding, what MQA Ltd calls core decoding, provides what I consider to be about 90% of the MQA benefits. Decoding in software unfolds / unpacks the music to a maximum of twice the base sample rate, 88.2 or 96, for either analog or digital output.
EQ, bass management, and other non-MQA DSP can take place after core decoding.
Using the real world example above, the Tidal desktop application, Audirvana, and soon Roon would decode the MQA 24/44.1 distribution file and unpack it to 24/88.2. This can be output digitally to any DAC, digitally to an MQA DAC for rendering, or output as analog audio.
Another example can be seen when streaming Beyonce's album Lemonade. The MQA distribution file is packed to 24/44.1 and the decoded file is also 24/44.1. The album must have been recorded at 24/44.1 and the studio is being honest with us, rather than upsampling it to 88.2 or higher.
When a master is 44.1 or 48 kHz, the core decoder Authenticates, decodes full dynamic range and matches to the current PC playback settings. (Depending on the soundcard and audio configuration, the Tidal App may decode this example to 44.1k or a provide a compatible 88.2k output for smoother playlisting). If you select Passthough, the raw 44.1/24b MQA file is passed downstream to a decoder. For music where the original sample rate is 88.2k or higher, the core output is always either 88.2 or 96kHz.
Note that other Apps and products implementing Tidal may be subtly different.
Software / Core Decoding with Hardware Rendering
The third way to play MQA music is through a software decoder and a hardware renderer. As you read above, MQA has three process required for the full MQA experience, 1. Full Decoding, 2. Software / core decoding, and 3. Rendering. In this method of playback, a combination of software and hardware is used to deliver all that MQA has to offer. Don't ever use this as the answer to an MQA exam question, but you can think of it this way - software / core decoding serves up the file and hardware rendering hits it out of the park.
Everyone looking to get the best sound from MQA music will want to use this method or the all hardware method discussed last. In this method, the core decoded MQA file is passed from a software application to the MQA hardware renderer.
Using the real world example above, the Tidal desktop application, Audirvana, and soon Roon would decode the MQA 24/44.1 distribution file and unpack it to 24/88.2. This file is output from a computer via USB or S/PDIF or even a phone via Lightning or USB on-the-go, to the hardware renderer. For this example, we'll output via USB to an AudioQuest DragonFly. The core decoded file enters the DragonFly at 24/88.2, then expands to the full 24/352.8 kHz resolution of the original studio master file.
Readers familiar with the DragonFly will know that the DragonFly supports audio up through 24/96. However, that's only on its USB interface. Internally the DAC goes up through 768 kHz. MQA enables the audio to duck its head to get under the door frame, before standing straight up once again. Kind of like a balloon as well. Squeeze the middle of a long balloon and the two ends will get larger while the middle shrinks. The two ends are the studio master file and the fully decoded MQA file, while the middle is the packed undecoded MQA file.
The above method is a really good way to work around the lack of USB Audio Class 2 driver support in many Windows operating systems and to get around interface sample rate limitations. It's possible to play 24/352.8 on a class 1 device and without custom drivers.
What happens when using software / core decoding and hardware that's capable of full decoding like the Meridian Explorer2? If desired, it's possible to use an app like Tidal to do the core decoding and send the MQA signal to the DAC for rendering only. If the Explorer2 is fed with an MQA core (decoded) signal, it only does the rendering.
Note about renderers: There are no generic MQA renderers, as each one is custom designed for each piece of hardware. According to MQA Ltd, the analog output is custom tuned for each device to most closely recreate the sound heard in the studio. As always, you'll have to be the judge to see if the marketing matches the end result.
One additional piece of information that fits somewhere between this section and the next, systems like Meridian that run digital to the loudspeakers, send a core decoded stream to the speakers before final rendering separately for each drive unit. This core decoding takes place in hardware / software loaded on Meridian hardware.
Full Decoding (Hardware Only)
There's not much more to say about this one. Full decoding is only possible in hardware and it's considered the full monty. Both aspects of core decoding and rendering are controlled by a single manufacturer and the requirements for third party software are gone. The final analog output however, is theoretically identical to a software / core decode and hardware render. We'll have to see once more opinions come in from people testing both methods.
A DAC or home theater processor capable of full decoding can receive an untouched MQA file (distribution file or stream) or a core decoded file from a software decoder, for rendering only. I'm not sure why anyone would prefer to use a software decoder when s/he has a full decoder in hardware, but it's entirely possible.
All details about the renderer hold true for a full decoder. Very custom and tuned to each hardware device.
A note about this tuning for each DAC. I've talked to many manufacturers who have products in the process of MQA certification. Every one of them says the process is thorough and a bit demanding, often requiring many updates to hardware and firmware until everything is as close to the target as possible. This piece isn't marketing, it's all based on engineering.
Using the above real world example, any software or hardware capable of sending a bit perfect audio stream to an MQA DAC with a full decoder, will work just fine. The DAC must see either a core decoded stream or undecoded stream without alteration.
Let There Be Light
Whether playing MQA content fully decoded, core decoded and rendered, or just core decoded, an MQA DAC or application will always signal the file is true to what the record label released. If it's MQA it will illuminate a blue/green light.
When I first investigated MQA I knew the blue authentication light on MQA DACs was helpful in identifying bit perfect output to the DAC, but I thought the whole authentication piece was unneeded. However, I've since learned that the music supply chain is full of challenges and less than stellar versions of our favorite albums (some related to up/down sampling). Much of this isn't malicious, it's just a matter of large companies with many people involved who may not know exactly what's going on. MQA has the ability to provide record labels with a single deliverable file and the consumer can verify this is the file s/he plays back at home. It's a cool concept.
Enjoying MQA music isn't rocket science, but it takes a little education to make the right choices. Obtaining the best quality MQA playback requires either a combination of software decoding and hardware rendering or a full decoding DAC. Fortunately, I believe 90% of MQA's benefits can be realized by only using a software decoder, called core decoding. Now that some of our favorite music is available in MQA, it's time we listen for a while rather than talk over the music. Set your systems up right and press play.