Proper Digital Audio Playback

The PonoPlayer got it right, whether they survive as a business or not.

There is a right way and a quick way to build a digital audio playback circuit.

The following information comes from Charlie Hansen, the designer of the Pono audio chain, and the excellent review by Tyll Hertsens. I’m putting it into it’s own post so other audio device builders get inspired.

  • EVERYTHING from DAC to jacks is DC coupled. No coupling caps anywhere.
  • Everything is TRULY balanced from the DAC chip all the way to the output jacks. There is no virtual ground needed, as we have true +/- rails from the switching power supply. The raw rails go to SUPER low noise regulators, of which there are a TON.
  • The audio circuitry has their own dedicated +/- regulators.
  • All of the digital circuitry runs off of positive voltage only
  • Three or four separate dedicated regulators there — one for the audio master clocks, another for the digital side of the DAC chip and a third for the rest of the digital circuitry.

“NOBODY builds portable players that are fully-discrete, fully-balanced, and zero-feedback. This all makes a huge difference.”

— Charlie Hanson of Ayre Audio

That’s what happens after the DAC, in the analog stage.



Regarding the file quality and DAC behavior before the analog stage, we have more details from Charlie:

 

  • Brickwall filtering creates massive time smear.
  • The human ear/brain is already known to be exquisitely sensitive to time smear.
  • DBT and AB/X are really only sensitive to differences in frequency response. Using these tools for anything to do with music is like pounding a nail with a screwdriver. Ain’t gonna work.

Specifically, one of the massive benefits of a higher sampling rate is not extended bandwidth.

Instead, it allows for gentler filters to be used.


In the case of the Ayre QA-9 A/D converter, the anti-aliasing filters have zero ringing or time smear for double and quad sample rates. (Only one cycle of ringing for single rates — something has to give somewhere…)

When Ayre designed the PonoPlayer’s audio circuitry, we held back nothing.

We gave it everything that could fit within the constraints of the budget, physical space, and battery life.

Every single secret we discovered went into the PonoPlayer. The digital filter is taken directly from our own products.

Guide To Hi-Res Audio

The momentum continues, as more publications pick up on this new push towards quality in consumer audio.  MP3 won’t die without a fight, but it’s 15 year grip on the music industry appears to be loosening.


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Check out the Consumer Technology Association’s Guide To Hi-Res Audio for a nice wide overview of the hi-res music market as it stands now.

 

The Resolution Wars

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Visual representation of “lossy”. These pixels are what is lost when this image is compressed using mpeg.


MP3’s are dying, thank god. MP3 is a transitionary technology that has overstayed it’s welcome. If you believe lossy MP3 is all you need for music, goodbye. Come back when you want to listen. Yes 320k is better than 192k or 128k. Yes it’s getting close to CD quality. It’s still less than half the data (Not to mention CD is 37 year old digital technology!). MP3/MP4/AAC is a lowest common denominator. It has no place in a discussion about quality.

CD quality is 600-1400k so you can just get CD quality these days, even streaming with Tidal. Once you leave the world of lossy and get to real resolutions, you won’t go back.

Confused with all the combinations of bit depth and sample frequencies available: 16/44, 24/44, 16/48, 24/96, etc.?

So what do you need?  Avoid buying expensive 16 bit. Don’t pay new prices for it, unless it’s the best that material ever hopes to be released at. Demand 24 bit versions and pay full price for 24 bit versions.

  • 24/44 is awesome enough for The Beatles and The Cars, two amazing bands
  • 24/88 and 24/96 are the emerging standards for hi-res audio
  • 24/192 is the highest resolution anyone works at and is starting to become popular

I haven’t heard 16/48 in 20 years but I can assure you that 16/44 is not able to deliver the full audio signal -if- the material is from higher resolutions or analog masters.


 

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One part of one inner ear – the most amazing vibration detector I can imagine. Every component does multiple tasks with such detail and subtlety that some of our finest machines could only hope to match it some day.


To spell out audio resolutions in human terms: you need at least 18bits of space to store the data and you need about 30k of undamaged samples per second.

If they had a format of 20/60 it would have been perfect for CD, but they didn’t, so we have to overshoot a bit since the format is just the container. The music is the content and you don’t want the container smaller than the content. In 1977-78 when the CD was being designed, this was a necessary compromise for reasons that have long since expired.

This 18/60 threshold is about the total of what we can detect as humans, so to me, 24 bit is the indicator of true high-resolution audio.  Higher sample rates might give you slightly more detail and audio data, but to my ears 24 bit is the primary upgrade.


 

There's a lot going on inside your ears.

At a micron level inside of the human inner ear. There are thousands of these tiny hairs positioned into arrays at multiple depths, each able to detect certain frequencies and timbres. Each hair sways, the entire mechanism can move, and opposite this area there is a mysterious fluid that appears to defy physics while it adjusts it’s location and density based on the sound. Some researchers believe this fluid performs a liquid-based form of compression/limiting/expansion as well as EQ and is controlled by still unknown forces. That’s serious resolution right there – self-organizing liquids and moveable micron-microphone arrays?  320k/sec is not holding that, nor is 1400k/sec.

It’s Bandwidth, Stupid

Everything digital boils down to bandwidth

  • how much you have
  • how much can you use
  • how fast the data can move through it

Bandwidth comes in several forms. The network connection is the obvious one because we already use the term bandwidth to describe this. This determines how fast one computer can communicate with another computer through a network.

Storage space is another form of bandwidth, if anything needs to be stored. Even streaming files through the network will require some local storage and files saved to your device require space. There’s the raw space, and also the read/write time of the storage volume – both are a form of bandwidth.

There’s plenty more places to measure bandwidth inside of, and plugged into, the computer such as the motherboard busses between the various chips, the ports in and out of the computer, and the video output. All of these have a known bandwidth and engineers must take this into account when designing circuits.

If it's digital, it's a "computer". This shows the motherboard and the components of the early CD player.

If it’s digital, it’s a “computer”. This shows the motherboard and the components of the early CD player.


 

The entire digital audio format debate boils down to bandwidth.  How much sound bandwidth can your body pick up?

37 years ago when Phillips & Sony were working on the audio CD they knew that bandwidth would be a major issue. Digital audio generated very large file sizes and required lots of bandwidth to reproduce accurately. 50mb was literally HUGE in 1978, and that’s only 1 5-minute song on CD. This is a time when $500 hard drives were 10mb! The draw to the optical disc was the huge storage space it provided on cheap plastic discs.

Which brings us to the bandwidth of the disc and file format selected. The new CD design could hold roughly 600mb of data. What resolution to store the audio as became the driving force in finishing the standard, with engineers deciding a nice compromise was a 44k sample rate stored in 16bit files, allowing for about 60 minutes of runtime per disc, or just enough to hold the president of Sony’s favorite symphony (a rumored requirement of the new format).

This is the thing: bandwidth = cost.  More money gets you more of it, especially in components. Want a motherboard with higher bandwidth? Costs more. Want a chip with higher bandwidth? Costs more. A port and cable that can move more data? Costs more.

So the engineers and designers of the CD knew there were better quality resolutions than 16/44, but the overall cost of making a player to play higher resolutions, and total bandwidth of the storage for them, just wasn’t there in 1980’s tech.  Early digital production systems did use 20bit audio with sample rates from 40 to 88k, but they were expensive and specialized, not for the consumer.

 


 

 

By the 1990’s the price of higher-bandwidth components had come down enough to attempt a format upgrade, but like many things in the 90’s, the internet changed everything.  Instead of consumers moving to a new optical disc holding higher-quality files and played through better players (SACD), the trend was to smaller, mobile files that could be moved around the internet and played on smaller and smaller devices.

The visual engineers who developed the JPEG compression format stepped in and put together an audio specification for shrinking CD-quality files down to something 90’s era computers could handle. This became known as MP3, and at first it seemed magical. How could that 50mb song from a CD become 5mb and play back almost perfectly from my hard drive? Impressive.  Overall sound quality was deemed “good enough” because of the huge boost in convenience mp3 provided.

As we lived with MP3 and listened closer, many consumers were less than impressed. But time marched on, napster was built to trade illegal MP3, iPod shipped, then smartphones and tablets, and MP3 became the new consumer format in the early 00’s.

This, of course, is not the first time we consumers have taken a quality downgrade in the name of convenience.

 


 

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The deets on bandwidth used. Netflix HD shows how much more video (TV+film) is valued compared to music. Netflix will be 4k soon, perhaps the 7th upgrade to consumer digital video as compared to no upgrades to digital audio.

 

Now is now. Almost all limits of bandwidth from the last 30 years are gone, as is evident with Netflix streaming everywhere, people running very fast computers packed with memory and fast storage on broadband network connections. There are now millions of servers talking to hundreds of millions of devices, each little device packing more bandwidth than a $50,000 computer from 1980.

The bottom line – We no longer need to reduce the art to fit the distribution. If an artist makes a record at 24/192 you should be able to buy it, store it, and play it at 24/192.  If you want a lesser version for a lesser device/use you can easily make it yourself.  If the artist makes the record at 16/44 that’s fine too, buy that one.

The point is that reducing from the audio master was only done in the name of bandwidth restrictions that are now gone.

 

We can store 100's of full-quality albums on this tiny card.

We can store 100’s of full-quality albums on this tiny card.

 

 

 

Recording Quality Rule Of Thumb

Allow me to speak some truth about the recording arts — the overall quality of music production has been going down since before I started. I’ve done nothing to reverse the trend ;-).

This is due to multiple factors not least of which is the march of technology and the reduction of overall recording budgets bootlegging has brought us.

How much would you spend on producing an album that most of your actual fans won’t even purchase?

Continue reading

40 Years of Recorded Music Distribution

Vintage baby

Vintage jams

Quick history lesson —

Digital audio made it’s public debut with the CD standard known as “RedBook”, started in 1978. A collaboration between Phillips & Sony, the CD standard was originally going to be 14bit/40k with error correction and ship on a 115mm disc, but Sony pushed for 16bit/44k with no error correction. A VP of Sony also pushed to increase the total run-time from 60 minutes to 74 minutes, warranting the disc be enlarged to 120mm, and ruining Phillips’ early investment in a plant already printing the 115mm discs! Corporate intrigue for sure.

The RedBook standard was finalized in 1980 and CD players started hitting the shelves by 1982. To this day RedBook is owned by Phillips and costs a manufacturer over $300 to download the specifications. Why the name RedBook? The engineers compiling the specifications did so in a red binder. Engineers aren’t known for creativity ;-).

In the marketplace, the new digital CD’s had numerous advantages over the two existing analog formats of vinyl albums and cassettes. To list a few: no dust problems, little heat warping, less vibration-induced skipping, couldn’t unwind or tangle, vertical storage no longer needed, no replaceable stylus, not magnetic, liquid-proof, instant auto cue. Also there’s the indefinite duplication with no loss in quality on the copy or the original – that’s a huge advantage for digital.

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But CD’s did not clearly “sound better” than vinyl when all the other issues were addressed. Most of those issues are considered interference or physical media issues. None of them address how the actual recorded music is presented. All music sounds best live, as the microphone is not able to recreate our auditory system. Did CD’s actually sound “better” than analog once playback and media issues were addressed?

This has been a sticking point since the early 80’s. Many of us could hear something missing from CD’s, and it wasn’t just dust and motor noise from the turntable. It was the stuff that is nearly impossible to describe in words: reverbs and decays were different, the timbre of cymbals, voices, and stringed instruments were different, the mid-lows weren’t as warm or round, delays didn’t seem as present or accurate, the stereo-width wasn’t as obvious, the center was hard to find, the top was very pronounced and brittle, some complained of a boxy sound or a digital graininess.

The 1980’s didn’t just bring CD’s to market, it brought us personal computers and the early internet. By 1990 the same group that was working on the JPEG digital picture compression standard starting working on a media compression format. MPEG was designed for squashing CD-quality audio files small enough to stream on dial-up modems. By the mid-90’s the mpeg format was in use and competing with other early digital audio formats like RealAudio.

Now that the music could be squashed to an easily tradable size, piracy ran rampant. The late 1990’s brought us mp3 (after mpeg-1 and mpeg-2). Napster, peer to peer file sharing, bad DRM attempts (security on audio files), and ultimately led to a rapid decline of the music industry. Everything was being stolen and fewer hard copies were selling. The new mp3 files were perfect for trading online, and the novelty of this new convenience outranked the decline in sound quality. “Good enough” became the standard for sound quality.

Into this disaster stepped Apple, wisely seeing an opportunity to re-invent the personal audio player like the Walkman/Discman (stealing that market from Sony) and re-invent the record store (taking that market from traditional retailers). First they launched the player line “iPod” with it’s easy loading from your computer, then they opened the new record store with legal $1 songs and no-hassle purchasing.

Apple bet right and it took off (I bought music from there for a few years). I kept thinking I was getting ripped off though — where’s the hard copy with artwork that I can love, lose, find, loan out, break and buy another (or not?). All gone. Instead of our society going “paperless”, we went “album less”, to our detriment. We have been buying and streaming low-quality audio for over a decade now, and not always because of technical limitations.

That’s the end of this lesson, kiddies. The point here is that if you grew up in the mp3 era, you were listening to a compromise built on top of a compromise. 24bit HD Audio should be a revelatory listen for you.

 

The Challenge of Uncompressed Audio Formats

Good overview of the situation I’m heavily interested in (see “Save the Audio” section) – the battle between quality audio and convenient audio. Since the late 90’s most of us have accepted worse-sounding audio in the name of convenience, whether it be small mp3 files downloaded or even smaller mp3 files streamed – both pull more and more important audio out of the worlds music.

Neil Young’s Pono Service Illustrates Hi-Def Audio’s Problems.

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4k UltraHD Visuals Coming Soon – Where’s The Audio?

TV’s advance in resolution again – HD, 1080p HD, and coming soon 4k UltraHD. This thing can push 2160p to your eyeballs but it’s gonna cost you $5k for the small one, and $6k for the larger.

So this is the what, 3rd major format upgrade for TV in 15 years? Meanwhile we downgraded our audio format in the last couple of decades.

It’s a crying shame that music – which goes anywhere while encouraging activity, concentration, expression, and emotional fulfillment — is completely overlooked in the digital age in favor of again increasing our television performance.

Watching screens generally discourages activity, concentration, expression, and emotional fulfillment.

Shows where our priorities (ahem profits) are.

 

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Save The Music One Hertz At A Time

OK I have been listening to mp3’s for about 15 years now, and I have to say I’m ready for the next digital format. I want 96k minimum range (192k preferred) so it almost sounds as good as my albums. I want 24 bit so it makes my modern multi-speaker systems work at all volumes. I can cheaply have enough storage to handle it. I want my music’s emotion back!

WOODSIDE, CA - DECEMBER 15: CEO of Apple Steve Jobs sits at his home in Woodside, CA on December 15, 1982. IMAGE PREVIOUSLY A TIME & LIFE IMAGE. (Photo by Diana Walker/SJ/Contour by Getty Images)

WOODSIDE, CA – DECEMBER 15: CEO of Apple Steve Jobs sits at his home in Woodside, CA on December 15, 1982. IMAGE PREVIOUSLY A TIME & LIFE IMAGE. (Photo by Diana Walker/SJ/Contour by Getty Images)

I primarily listen to funk, rock, hip-hop, soul, and only a bit of classical, and I miss the full range of Bootsy’s bass, Eddie’s guitar, and Al’s voice. Friends who listen to opera, voice and classical probably avoid MP3 already, but the real culprit is the concept of “CD-quality”. This equals 16/44, and this is simply not sufficient in 2012. It was not even sufficient in 1973 when everything was analog. Only the convenience and laserness of CD’s convinced us that this was about as good as we were going to get. Real technical limitations of 1982 CPU technologies made it the best we could get cheaply.

This was 1982 people. The mp3 format is built on top of the CD format, and audibly it’s a disaster. We have nearly regressed back to the dynamic range of a 1920’s turntable. All those compressors (yeah you dubstep) just make it worse. Remember when the meters really moved?

If you could measure music’s emotional content in a data unit it would be clarity through it’s full range. The days of compressions built on top of dead formats should end.

michell_gyrodec_mki_courtesy-Michell-Engineering

I support any movement to improve the sounds entering our ears. All we want to hear is the same thing in the Steve Jobs photo above.

#SaveTheAudio

 

I Support Pono

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Neil getting full balanced goodness into his ears

I love this idea.

Neil Young finally got his wish to attempt to restore audio fidelity to our lives. They are calling the thing Pono and most of the press reports on it present it as a battle with Apple’s iTunes world (which is currently living on the 256k mp4 format).

But most modern ears miss the real battle Young is waging – Continue reading