Still cold from the UPS truck the Apple HomePod woke up when I plugged it in and asked my iPhone for a dance. They spun about and chatted in their local network for a minute or two before Siri introduced herself. It was completely unexpected surprise from a great friend who shares the love of music. A day into the journey I have a few thoughts.
I'm a poor musician, but find it an important part of my life. Grad school was at Stony Brook. Besides an excellent physics department one of my reasons for doing grad school at Stony Brook was its proximity to music in New York City.. That wasn't quite enough, so two of us founded a concert series at the university that thrives to this day. At Bell Labs it became apparent that music might be a significant driver for Internet use and I found myself walking several paths. One was sound field reconstruction.
Sound field reconstruction is just the fancy way of recreating the sound where it was recorded or engineered in your home. In theory you record the acoustic signatures of the recording studio and your living room and create a mathematical operation that makes your living room sound like the recording space. In practice it's approximately hard. Sound waves are fairly large and get reflected, absorbed and transmitted by and through everything in your room. Making matters worse the sound field at different spots in the room is usually very different and things in the room move between and during listening sessions. We made serious progress, but it took exotic microphone and speaker arrays as well as state of the art (for the time) computing to make it sort of work.,
One detail is centrally important. Imagine sitting before a simple speaker cone. Most of the sound comes straight at you with the volume falling off as you get away from the speaker's central axis. Speakers have very characteristic patterns showing how loud they are depending on the angle you're sitting at as well as the frequency of the sound they're producing. If you have two stereo speakers there is usually a sweet spot where the sound reproduction is optimal. In this area the sound field can be fairly good and you can close your eyes and visualize where the musicians are.
Imagine an array of speakers, each with its own amplifier, all controlled by a computer, you can control the phase and amplitude (loudness) of each speaker. The waves they send out interfere with each other as they expand outwards. By controlling the phase and loudness (amplitude) of each speaker you can make them interfere in such a way that they create a new wave that can be aimed. The little animation shows an array of four speakers in a row, but it can be any number and they don't have to be in a line. The HomePod uses seven small speakers arranged in a ring.
(you may have to click on the animation to start it)

The HomePod also has a ring shaped array of six microphones. They listen to the room (sample it) at a fairly high rate and decide what parts of the music, from its stereo signature, need to go where and how it needs be modified to interact with the room and everything in it. An Apple A8 processor, the same two billion transistor processor used in the iPhone 6 and 6 Plus, handles the computational chores. This is much more power than we had back in the day. Although I don't know exactly what they're working on, several people I know who are real experts at this have been at Apple for years.

The HomePod also has a computer controlled single woofer with its own amplifier mounted vertically to handle the low notes.
I'll leave the specsmanship, mechanical and most of the UX discussion to others and just talk about what it sounded like. I'm not golden eared, but rather a serious listener. I focus on the music and let it take me where it pleases.
I listened to works across several genres with the HomePod placed at about ear height in a small acoustically complex room.1 For very small groups - soloists and piano quartets for example - the sound stage was excellent .. about as good as my stereo pair of conventional speakers (about $3,000 in speakers). The HomePod didn't match the reference speakers when I was sitting at the sweet spot, but was better when I moved around the room. That is astounding.
It was creating stereo -a term has nothing to do with a pair of anything, but rather three dimensional. Moving beams of audio around it was painting a sound field in my living room.
As I listened to larger ensembles I found a less accurate sound field. That said it was still comparable to my reference pair when I was away from my very small sweet spot - its effective sweet spot was larger. Note for some pieces of music a good $500 pair of speakers would do a better job if properly installed, but would love to see what a pair of HomePods placed about two meters apart would do. Apple has promised the feature will be available later this year. I've already earmarked the funds for immediately buying a second unit then. I suspect a pair of HomePods will blow my reference pair away when it comes to sound stage placement. That will be even more true for those who haven't carefully adjusted their current speakers with test recordings and a spectrum analyzer.
You can control it from an iPhone, iPad or Mac, but Siri is the intended interface. I've had poor luck with Siri on my iPhone, but here it works much better. It's also much more robust to interference. Microphones beamform too and it's clearly listening to you doing its own cocktail party trick. That said it, and every other interface I've seen are just wrong when it comes to classical music.
Comparing it to the networked speakers from Amazon and Google is silly. Their speakers are terrible and useful only as acoustic wallpaper you listen to in the background. They're really microphones in your home listening to you assuming you agree to Google's or Amazon's value proposition (I don't). Privacy is vastly different - I'll go with Apple's differential privacy rather than Google's "you are the product" flavor. But if music is secondary and you want a digital assistant with a speech interface, Google and Amazon are the ticket. Apple is going after the other audio companies along with making its platform stickier in the process
I suspect the speaker will be like the Apple TV - fairly stable hardware with the bulk of improvements coming through software updates. My list of UI and UX issues is growing, but I suspect this will become part of my life.
And a final caveat - speakers involve personal taste. YMMV
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1 I'm very familiar with these pieces. With one exception I've heard them live and I've even been involved in the recording process on two.
Ecstacy Anonymous 4 and Mike Marshall
Us Regina Spektor
Seven Swans Al Petteway
The Heart Asks for Pleasure First Ahn Trio
Black Horse and the Cherry Tree K.T. Turnstall
The Littlest Birds The Be Good Tanyas
Submarines The Lumineers
Pipeline (electric and acoustic versions) The Duo Tones
An Spailpin Fanach Connie Dover
The Heroic Conditions of the Universe Pt 7 After the Storm Alexandre Desplat
Turn it Around Lucius
Jolene Mindy Smith's version
Vespro della Beate Vergine: Domine ad Adiuvandum a 6 Monteverdi
Shchedrik Kitka
Our Town Iris DeMent
Sun Will Set Zöe Keating
Don Giovanni Madamina, IL Catalogo and Questo Mozart (sort of a sign of politics)
Canon a due Violincelli in D Major Gabrielli
Cello Sonata in D Major Op 69 Beethoven
Suite No 6 in D Major JS Bach (Yo-Yo Ma)
beyond 88
Yesterday Om pointed out that it was piano day - the 88th day of the year honoring the 88 keys of most pianos. I read his post a day late, but there's still hope for another celebration with the same name. An obvious choice might involve the Bösendorfer grand where options include 92 and 97 keys in addition to the normal 88. Music has been written for these beautiful instruments, but why stop there?
Press a key on the piano and a hammer strikes one or more strings which begin to vibrate producing a sound. The frequency of the vibration depends on the length of the string with longer strings vibrating at lower frequencies.1 The left most key causes the longest string to oscillate 27 times per second - 27 Hertz (Hz) - while the right most key produces a 4,186 Hz frequency. In between the keys are divided into 7 octaves, each composed of 12 keys. Each octave doubles the frequency so the C above middle C has a frequency twice as high. The notes are evenly divided so each key has a frequency 21/12 times - just under six percent higher than the preceding key.
Now we're ready.
Let's say you wanted a piano with the range of human hearing - usually given as 20 to 20,000 Hz in young children. Going from 4,186 to 20,000 Hz, after a bit of arithmetic, requires 27 extra keys on the right. Five keys on the left will get you to 20 Hz.. One hundred and twenty keys and some long arms would be sufficient to entertain young children to the limit of their range.
But what about dogs? Canine hearing goes up to about 40,000 Hz. All we need to do is add an octave, or 12 keys, to cover their range. Other mammals can hear even higher pitches. Bats top out around 160,000 Hz so we add two more octaves giving us a 156 key instrument. We don't have to go much higher as the atmosphere strongly attenuates higher frequencies. A bat can produce a very loud noise, but even their sensitive ears are only good for a 20 meter range.2
We've left out elephants which go down to about 12 Hz - that works out to 9 keys on the left. We've grown the beastmaster piano to 165 keys. I won't cover whales because pianos don't work underwater.
The game can go on. There are any number of natural sounds of lower frequency (infrasound), but we'll leave it at that..
Well - almost. There are very faint sounds in the universe - ripples that move compress and expand space-time itself. They come across a wide range of frequencies, but exquisitely sensitive instrumentation is required for some of the loudest - like colliding black holes where the energy that goes into the resulting gravity wave can be the equivalent of several solar masses. It turns out the frequency of the first one detected was a chirp that went from about 35 Hz up to about 250 Hz (close to middle C). You can play the signal as audio.
So much information there, but it may not be pleasing so let's end with one of the most demanding pieces for the human voice - in this case a coloratura soprano. The Queen of the Night in Mozart’s Die Zauberflöte.
I'll leave you to find some good piano music today. Perhaps Om's list is a place to start.
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1 It also depends on the mass of the string, its diameter and tension. Additionally a rich set of other frequencies are produced giving the louder central frequency richness and character. There's a good deal of art in the design and construction of a fine piano and none of the sound the same.
2 It's a feature. Longer range would confuse them with signals from other bats, plus they tend to work a few meters from their prey.
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