The Exploratorium - a unique museum of science, art and human perception - is still two months away from its grand reopening. The lower floor is strewn with half-built exhibits and criss-crossed with caution tape. The upstairs is a buzzing office full of people planning for the big day and beyond. This vast new space on Pier 15 in San Francisco opens to the public on April 17.

But on Monday the museum released Sound Uncovered, its second free iPad app, which the creators showed me during a visit to the unfinished museum. As I explored the app's exhibits, the tablet disappeared in my hands. When you launch this app, you're in the museum, no matter where you are.

Everywhere Is A Laboratory

The design of physical Exploratoreum starts with the goal of creating an experience and builds up from there. An iPad is just as good as a room in the museum if it's the right place to focus the experience of an exhibit. "What makes the Exploratorium a unique place is that it's the combination of a museum, a laboratory, and a developmental studio," says Rob Semper, executive associate director of the museum.

Semper is a physicist whose tenure at the Exploratorium goes back to designing some of its original exhibits with founder Frank Oppenheimer (also a physicist, who worked on the Manhattan Project with his older brother Robert Oppenheimer). Semper took a little time off from the Exploratorium to run the collaboration between Apple and Lucasfilm. Now he's back creating museum exhibits again, both in San Francisco and at partner museums around the world.

Extending its exhibit design to the iPad is a natural move for the Exploratorium. This museum came online in 1993, making its website among the first 600 in the world. The Exploratorium is like a laboratory for turning things into laboratories. In the same way it is turning its new U-shaped port building and the walkways and docks outside into a delightful maze of science experiments, it can turn flat, pixellated spaces into exhibits as well. And on the iPad, these experiments come to life, gaining the inputs of touch, movement, light and sound.

It's All About Perception

The two Exploratorium iPad apps so far are both "buffet-style" collections of short, multi-sensory exhibits. You can select from a table of contents or swipe through like a magazine. The first was Color Uncovered, which uses properties of the tablet's display to demonstrate properties of light. The new app, Sound Uncovered, uses both the speakers and microphones, as well as text and video explanations, to show off some of the surprisingly bizarre properties of sound.

"Perception is a strong subject for us," says Sound Uncovered project director Jean Cheng. Designing a museum exhibit at the level of user experience comes right down to perception. "This app is about sound, but it's really about you." By causing you to notice weird things about your perception that you usually take for granted, the Exploratorium forces you to think more critically about your environment, and it does so purely through fun.

I'm not going to spoil the illusions for you. If you have access to an iPad, you should download Sound Uncovered for free and try it yourself. Right now.

But I will tell you about my favorites:

I love "Find the Highest Note," which presents a circular organ and demonstrates the mind-bending auditory Möbius strip known as the Shepard scale. As you move upward and downward in base pitch, the eerie Shepard tone's partials replace each other at the top and bottom range of hearing. As a result, even though you're moving up or down in pitch, it ultimately never sounds like it's getting higher or lower. It's the auditory version of the barber-pole illusion, where the corkscrewing shape seems to move upward or downward forever while remaining in the same place.

What's also cool about this exhibit in the app is that it doubles as a musical instrument.

Another great social exhibit is the "How Old Are Your Ears?" test, which lets you slide down from an inaudibly high frequency into the ranges that humans naturally lose the ability to hear over time. The younger people in the room will start to hear an ear-splitting whine, but the elders won't hear a thing until lower down.

As we ran through the illusions at the museum, the construction crews periodically tested the fire alarm in the building, which pierced through our conversation. It was uncomfortable for a second, disrupting this carefully arranged social situation, but then we realized the building itself was demonstrating the very kinds of sensory and cognitive tricks we were playing with on the iPad.

Simply Social

The Exploratorium is not afraid to take risks with its apps. One exercise in Color Uncovered asks the user — with plenty of caution — to put a drop of water on the screen, which creates a magnifying bubble in which one can clearly see how pixels work. The team laughs about some of the App Store reviews they got from people who didn't handle that part carefully.

But the apps are simple and magazine-like, going out of their way not to overwhelm people less used to figuring out how iPad apps work. "We don't want to further mystify people with this tech," director of online engagement Lowell Robinson says. "Frank [Oppenheimer]'s dream was to demystify people about how the world works." Accordingly, these apps are not about deep-down, immersive virtual experiences. "We're trying to give you physical ways to test," says Cheng. The apps ask you to try things, try them on others, and pass the tablet around.

The Exploratorium apps are social, but not in the Facebook way. "Social in the old-fashioned sense where you're sitting next to somebody," Robinson says. We had a good laugh about that.

Sound Uncovered for iPad is available for free on the iTunes App Store.

Photos by Amy Widdowson.

The State of Online Music report contains some big, but not altogether unexpected numbers: More people are listening to music online and artists saw more activity on Twitter and Facebook than they did in 2011. Across a variety of online sources, the Play button was clicked more than 93 billion times, a 45% increase over 2011. Pretty impressive, to be sure, but not a total shocker. 

Triple Play

Perhaps the most striking chart contained in Next Big Sound's interactive report is the one showing how SoundCloud's user activity tripling over the course of 2012. The service was already enjoying healthy year-over-year growth throughout 2012. Then in September, it saw a massive jump in monthly plays per artist, and the trend line kept shooting north until the end of December. Of the music services tracked by Next Big Sound, it was far and away the fastest growing. 

What gives?

The service's growth was probably aided by a major website overhaul, which put more focus on user engagement with continuous track-by-track playback and added more social functionality, such as a retweet-style sharing button designed to help audio content spread across the service. 

SoundCloud's redesign may have been the company's biggest project of 2012, but it didn't eat up all of the team's time. They also managed to push out major updates to most of their mobile apps, forge a ton of new content partnerships and convert the service's default player to HTML5.

Fueled by a few hefty rounds of funding, these initiatives no doubt helped SoundCloud better position itself as a sort of "YouTube for audio." The goal, in the company's own marketing speak, is to "unmute the Web." 

YouTube Still Rules

YouTube itself was another enormous source of online music last year. It didn't see  spikes as dramatic as SoundCloud's, but for most of the year, the video behemoth delivered more than 20,000 average monthly views per artist, in some months quadrupling what artists saw the previous year. 

Indeed, YouTube remains a much bigger source of music than SoundCloud, but the growth of the Berlin-based startup  is remarkable enough to make it serious contender in the online music space. 

Don't call it a Spotify killer either. For whatever reason, Next Big Sound's report doesn't include data from the dominant subscription service, but regardless of what the numbers say, the two companies' models are very different.

The Independent Alternative

For one, SoundCloud doesn't have to contend with the gargantuan music licensing costs that subscription services like Rdio and Spotify do. Whereas those services boast content deals with all the major labels and big indies, SoundCloud has a much larger selection of unsigned, under-the-radar musicians, remix artists and DJs. Indeed, about two-thirds of SoundCloud's fan activity in 2012 was centered around independent and unsigned artists.

What will ultimately become of SoundCloud? It's tempting to envision it getting gobbled up some Web giant like Google, but for now it's focused on building out a massive trove of content, weaving it all into the Web and making it easier to share. The "YouTube for audio" analogy looks increasingly apt, especially if its metrics continue to shoot skyward. 

The most striking change is how SoundCloud looks. It sports a cleaner, more app-like interface with a vastly simplified navigation. Instead of five top-level navigation buttons, it now has just two, flanked by a much more prominent search box. 

Beyond Looks: How SoundCloud Works Now

It's a huge visual refresh, but the aesthetics are practically a footnote to what's really new here. The entire service has been reengineered to fundamentally change the way people interact with it. Audio now plays back continuously as you browse the site, even as you jump from page to page. When one track ends, the next one in that user's audio stream begins. SoundCloud is also going live with a feature called "sets," which are basically user-curated playlists that exist in a single waveform. 

Another key feature - new even to beta testers like myself - is the Explore tab. It's here that SoundCloud hopes to connect users with the content creators who are collectively publishing 10 hours of music, remixes, radio shows and audio commentary to SoundCloud every minute.

It's this lean-back, no-clicks-required listening experience that the company hopes will keep people engaged, spending their work days with SoundCloud instead of something like Pandora or Spotify. So far, it appears to be working. Since launching the private beta of this redesign in May, SoundCloud has seen a 30% increase in engagement. 

"This will be the biggest update we've ever done in terms of core metrics," says SoundCloud cofounder and CTO Eric Wahlforss. In addition to the juicy 10 hours-per-minute audio upload stat, the company now boasts a reach of 180 million users. That's overall reach, not registered users, a metric Wahlforss says the company focusing less on these days. Wahlforss won't talk about revenue or the number of paying, premium subscribers, but he says the freemium model is working out.  

The site's massive overhaul coincides with the company's other big strategic initiative: courting radio programs and other audio content providers beyond the musicians, DJs and remix artists who have populated the site from day one. This summer, SoundCloud hired public radio vet Jim Colgan to oversee content relationships, and the platform is increasingly beloved by journalists. The company stops short of using the term "radio" in its marketing efforts, but you can see how SoundCloud could slowly carve out a key role in that medium's future. 

SoundCloud Grows Into a Truly Social Platform

Continuous playback is nice (and some might say, now a fairly standard feature on music sites), but it's not enough to keep people tuned in. There has to be some intelligence behind what content is playing and why. To achieve that, SoundCloud is becoming more social, leveraging Facebook user data to connect users with the most appropriate sound creators and building in some Twitter-style interactive features of its own.

Starting with the sign-up screen, the Facebook integration is tighter. When you authenticate using your Facbeook account, SoundCloud scans your likes and tries to figure out which record labels, radio programs, musicians and everyday users you might want to follow. Again, this is fairly standard stuff for a social service (and the lack of a Twitter friend-finder is surprising), but it's a significant step toward SoundCloud becoming not just an audio-hosting service, but a sound discovery engine as well.

"The better we know you, the better the stuff we can play for you," says Wahlforss. "I think the future is very much going in that direction: A highly personalized continuous playback experience powered by smart algorithms on the one hand and great curators on the other."

It makes sense. The more people you follow, the more relevant audio will playback and the longer you'll keep SoundCloud.com running in one of your browser tabs.

It's not just about integrations with existing social services: SoundCloud is slowly positioning itself as a social network in its own right. The site has long encouraged collaboration and interactivity through standard "likes" as well as time-based comments that can be posted at any point in an audio file's waveform.

Today, it takes things up a notch by adding a "repost" button that lets users share each other's sounds as they would on Twitter or Tumblr. That's great for discovery and user engagement and thus good for SoundCloud's longterm prospects. It's also potentially huge for sound creators, whose bedroom-produced remixes might - just maybe - get reshared by Snoop Dogg. 

Back in 1958, though, sound was not so easy to create and play with. But the then relatively young medium of radio demanded sound effects like gunshots and new music for a growing line-up of audio programs. To meet the needs of show producers, the BBC launched the Radiophonic Workshop, a sound effects lab where musicians and sound engineers created fake gun shots by slapping rulers on a table, used analog tape loops and built pre-synthesizer sound effects machines. 

Interactive, Web-based simulations of those early machines are now available, thanks to the BBC's Research & Development Department, which recently launched a fascinating prototype showcasing four digital noisemakers. The fun site features a gun-shot sound effect generator, a pre-synthesizer "wobbulator," a trio of tape loop machines and an early ring modulator, which was used to generate the robot voice on the original Dr. Who. 

No Flash Required

For each retro sound-making device, the site has historical information, a live simulator demo and the source code used to create it. The kicker? It was all built without a touch of Flash or anything other than open, cross-device-friendly Web standards. The team at the BBC utilized the Web Audio API, which uses JavaScript to process and synthesize audio in the browser. It's the kind of thing developers once had no choice but to rely on Flash for, but is now easily achievable using lighter weight, more open technology.  As for the interfaces, those were done using frameworks like backbone.js and jQuery, alongside custom-built elements developed in house at the BBC. Each demo has a detailed technical breakdown showing how it was built. 

This is awesome. Not just because it gives us fun little browser-based synthesizers to play with, but because of what demos like this mean for the Web. For the last two or three years, developers have been moving away from clunky, proprietary technologies like Flash and Silverlight and, whenever possible, using HTML, CSS and JavaScript to build complex interfaces and embed multimedia. The result is a smoother experience that works across devices and browsers without the need for extra plugins. 

And yes, simulating old-fashioned gun shots using a graphical UI in the browser while you should be working? That's cool too. 

But what about audio? The Web could really use a universal "listen later" button. 

I Can't Live Without Time Shifting

I don't know what I would do without the ability to time-shift the content I encounter online. Throughout my day, I come across blog posts, long-form articles and videos that pique my interest, but have nothing to do with whatever I'm working on at that moment. Thankfully, the Instapaper browser booklet allows me to set aside each article, neatly filing it away for later consumption and, perhaps more importantly, keeping my mind clear of distractions. Without this, I would go insane. 

In addition to my ever-overflowing Instapaper queue, I have a queue of videos that sits in the Boxee iPad app, just waiting to be AirPlayed to my  HDTV over dinner later. What I don't have, however, is a way to save audio content for later listening. 

Truth be told, there are several ways to save certain types of audio content so they can be heard in the future. NPR's iPhone app lets me queue up news clips and episodes of shows. Podcasts, almost by definition, are queues of audio for later listening. If I favorite a track on SoundCloud or like a song on YouTube, I can return later to that list of clips and hit play.

It's possible to save audio, but the options are fractured across different apps, platforms and devices. Why can't we have a universal "Listen Later" button like the "Read Later" bookmarklet we use for text? 

Some Promising Initiatives, But No Slam Dunks

Some developers are taking a stab at it. Andrew Kurjata, a self-described "radio guy in a digital world" used Tumblr and a Firefox plugin to build his own personal audio queue. It's a creative solution, but a multi-step hack like this probably isn't seamless enough for most people. Similarly, there's a workaround that will let you use podcast app RSSRadio in an Instapaper-like fashion, but again, it's a hack. A Web app called HuffDuffer lets you build out your own podcast RSS feed from found audio clips. It's nice, but still not quite the universal button Web audio needs. 

Some projects focus specifically on music. The inventive developers behind the Tomahawk music player created a browser bookmarklet that scrapes webpages for meta data about audio files it finds - and then checks that against its own mega-database of song metadata and lets users queue up those tracks in the Tomahawk desktop player. It's pretty brilliant from a technical standpoint, but it works only with music and has no mobile component. 

Minilogs is a Web app that lets you build playlists of songs from across the Web, a process that's simplified by its handy browser bookmarklet. It can pull audio from sources like SoundCloud, Spotify, BandCamp and YouTube to build Web-based playlists controlled by a simple, universal player. It's nice, but once again, it's music-focused. 

One of the most promising solutions for saving sounds is Later.fm. It's similar to Minilogs, but is more visually reminiscent of Instapaper and goes beyond music to include podcast episodes and other clips. Like most of these projects, Later.fm is still very much a work in progress, and that shows when you try to scrape audio from certain pages. 

Whoever Nails This Wins At Web Audio

Each of these projects is impressive and promising in its own right, but none of them are the end-all, be-all Instapaper-for-audio repository many of us are clamoring for. One of the reasons no such solution is exists is because audio is a far more complex beast than text. Text is text. Words don't have formats, codecs and complex licensing restrictions that inhibit them from being shared freely. Audio content has those variables and more, making it much harder shift it across time. 

Who will crack this nut? Apple would never come close, but Google might. More realistically, I could see a company like SoundCloud or Stitcher radio adding this type of functionality to their Web and mobile apps. NPR's tech team could surprise everyone and win itself major digital media points by pushing out a solution.

If any one of these entities finally gives us an Instapaper for audio, I can guarantee that I - along with many others, I'm sure - would spend a lot more time in their apps, interacting with their brand. Whoever solves this problem wins at Web audio.  

 Lead photo by Stephen Cummings.