In this guest blog post, Zatil Hamid of TI considers some of the algorithms and tools that are being added in to e-books to ensure a high quality listening experience for the end user.
Digital book sales at Amazon have now officially surpassed traditional paperback and hardback books, thanks in part to cool new e-book reader products like the iPad, Barnes & Noble's NOOK color and Amazon's Kindle. As more and more digital books are sold, I'm betting we're going to start seeing some pretty cool audio solutions make it into e-books.
Say you're listening to a book on your e-book instead of reading it. You could bookmark while you listen or mark where you stopped (don't you miss that feature from the old audio tape days?!), take notes, listen when you can't read, listen to classroom lessons, etc. And how about that traditional book club you keep missing because you don't have the time? Join in via video conference and have a book discussion on your e-book. I could actually join a book club. And when you're not in the mood to read or listen to a book - you could listen to some music.
Clearly, text-to-voice software isn't always going to cut it. Consumers want their listening experience to be pleasant, not be bored to tears by a droning robot - it has to sound good! People want louder sounds without clipping or saturation.
E-book designers can now deliver this with digital-to-analog converters and amplifiers that can output higher power to a given load and incorporate dynamic range compression (DRC) to maximize audio amplifier output capabilities. Typical music signals, for example, have a crest factor or PAR (peak to average power ratio) of 12dB. DRC allows the nominal power performance to be louder while increasing the output gain if the power level is low and reducing the gain when it detects a peaking or saturating signal.
E-book audio quality can also further be enhanced with additional digital processing. Audio filtering can be implemented using a programmable, scalable number of biquad and FIR filters to filter out unwanted signals from the 0-20kHz audio band. Some filters also allow adaptive filtering - switching between two banks of buffers storing the filter coefficients. Integrated digital signal processors can implement fully programmable audio enhancements prior to filtering that are either self-developed using user-friendly development tools or licensed algorithms from a third party. Audio CODECs like TI's TLV320AIC3111 also include powerful algorithms, like SRS WOW HD™, as a standard feature with no additional royalties or licenses required. SRS WOW HD™ takes compressed or uncompressed audio inputs and delivers wider sound fields, with high frequency clarity and deep, rich, bass response. I think of it as "unzipping" my audio listening experience.
Consumers are also always looking for longer play time for e-books - the need to have more efficient batteries is definitely helped by having more efficient, lower power solutions. For example, audio amplifiers that incorporate class-D amplifiers are 2x more efficient than class-AB amplifiers.
So how do e-book designers start integrating some of these "wish lists" into their products? The first step is to determine what kinds of applications that require audio support are being targeted. If multiple platforms serving different niche applications are being considered, then getting a comprehensive audio solution that spans the range of requirements would be helpful.
An added convenience is having access to a family of devices that are both package/pinout compatible as well as software compatible - you never know when you might need to upgrade, downgrade or access a different integration feature. For example, the TLV320DAC3100 is part of family of package and software compatible audio converters that incorporates everything from class-D speaker amplifiers and headphone amplifiers to the miniDSP.
We already have a pretty broad range of e-books out there from the utilitarian, basic electronic reader version to the Swiss army knife high-end tablet. As the volume of e-books continues to increase at a faster and faster rate each day, the cost for both e-books and digital book downloads across the board will continue to drop. This in turn will drive more interest from traditional paper book consumers, which drives even more innovation as even more people start to use different apps on their e-book. So, expect to see some sophisticated user experience advances like high end haptic integration and better screen technologies. Happy listening!