I spent a bit of time over xmas updating my iStethoscope iphone application (which links to The Undercover Scientist book) and adding many of the features requested by users. As usual, for those interested in the gory details, I'll explain how it works here.

The core features of the program remain unchanged, although I optimized the code to make it a little more stable. Please see the entry for version 1.1 and versio n 1.0 for details of how the audio processing works.

In version 2.0 I've added several major new features. The first and most significant is a shake-activated phonocardiogram. This appears if you give your iphone a left-right shake (that's a sharp movement in the x-axis accelerometer). It then replays the last 8 seconds of audio in a loop, while displaying the wave form and animating a grey bar to show which part is currently being played. The waveform is automatically scaled to fit, so eight seconds of quiet sounds will show a nice wobbly waveform, but a single loud noise may cause such a big spike that the rest of the pattern is scaled to nothing. To stop this happening when you've been listening to your heart and then remove the device causing a loud noise, the scaling ignores the last second of audio. So for best results when viewing the waveform corresponding to your heartbeat, hold the mic in place for 8 or more seconds when you can hear a clear sound, then remove and shake within one second. The phonocardiogram is cancelled with a second shake, and recording of audio begins again. Inevitably the resolution and sampling of the waveform is not perfect (there is only room to display 920 spikes out of 352800) so the display should be regarded as an approximation. Not all information can be shown, so the absence of a spike on the display does not mean there is none there. (The animation uses Layers - the waveform is written once into a bitmap called a layer and then that bitmap is redrawn over the new grey rectangle.)

Note that there's an iphone bug which affects all apps - if the iphone goes into standby for more than a minute while the program is running, the accelerometer is switched off. If you find the program does not respond to movements, restart the program and it should work again.

Another major new feature is a new mode: "Accelerometer." I added this mainly for ipod touch users who have no microphone and so can't use the other modes of the program. In "Accelerometer" mode, front-back vibrations (z-axis forces) are mapped to audio tones. A small movement gives a low tone, a bigger movement gives a higher tone. Sensitivity automatically changes according to the average movements, so several seconds of small movements will result in the iphone becoming more sensitive. This mode is more for fun than anything serious - there are too many interfering subsonic vibrations everywhere for you to detect your heart reliably in this mode. Because it uses the accelerometer to make noises, the shake-activated phonocardiogram is deactivated in this mode (the shaking iphone symbol disappears in the corner to tell you this).

The final change to the program is the addition of help images on the first screen (press the undercover scientist) and more hints in the pop up window about making the most from the program. I've done another youtube video below, enjoy! If you need help, leave a comment here and I'll post a reply.

Why Sh*t Happens: The Science of a Really Bad Day

Peter J. Bentley. Rodale, $16.95 (304p) ISBN 978-1-59486-956-3

Everyone has one of those days when nothing seems to go right, but why? Unlike others who have broached the question, British computer science guru Bentley (Digital Biology) actually escorts readers through a really bad day, exploring the science behind all the little things that can go wrong: he looks at why you slept through the alarm (to explain the nature of sleep); why you then slipped on the spilled shampoo (a look at the nature of cleansers and lubricants); why that torrential downpour soaked you on your way to work (a look at the cycle of water in nature). This journey through the day, if sometimes strained (getting chewing gum stuck in one’s hair on the bus), is a neat device for explaining the science behind everyday things such as how clothing is woven and why fabric is so strong (until it rips when you bend over) and how capsaicin in chilis fool the body and provoke a burning sensation. Each chapter ends with a brief tip on how to avoid future mishaps. Hopefully, readers and librarians won’t be put off by the title and miss Bentley’s reader-friendly explanations of the science behind everyday life. (Apr.)

My iStethoscope iphone application (which links to The Undercover Scientist book) continues to do extremely well in iTunes. It was the 11th most popular utility today out of over 700, with over 30,000 downloads in the last week. To celebrate I've created a second version which introduces a new listening mode: heartbeat pure. This uses different filtering to enable much clearer deep sounds, while removing all hiss and crackle. Although it may sound a little quieter that's because it's playing only the lower frequency sounds. I've found that it enables the 3G iphone to hear heartbeats much more reliably and count the heartrate much better than before. Using a good pair of headphones instead of the white earphones, you can also use the iphone like a real stethoscope and place it on your chest. (Remember the microphone is on the bottom, so that's the part that needs to be pressed to your chest.)

As before, for those interested, I'll explain how it works here. There are several minor updates in v1.1: The gain control at the bottom now automatically sets itself to the optimal level to help you listen without harming your ears. The first time the little undercover scientist appears, he gives instructions. I've adjusted the filter settings for "clear sound" to improve sensitivity. The link on the first screen to my book now works when you tap the name. But the main change is the new "heartbeat pure" mode. This uses an improved low- pass filter and no high pass filter at all. The result is that only very low frequency sounds remain audible and the resulting sound is much more pure and clean without any hiss. The 3G iphone suffered from hiss quite a lot, which prevented people from finding their heartbeats so easily and confused the heartrate monitor. Using this new mode, the heartrate monitor is much better, and it's much less fussy about accuracy with the microphone - you can still hear a heartbeat even if you are not so good at finding your pulse or artery. The downside to this change is that more processing is needed, so I had to increase the slight delay between the sound and playback fractionally compared to the last version. Users should also take care using the new "heartbeat pure" mode with volume and gain on maximum - if you brush against the microphone you may find the result very loud, and it might make the sound glitch a little. (You should restart the program if the sound continues to glitch.)

Hopefully everyone will enjoy the application, and remember that learning to find your pulse is a valuable skill. If you found the app interesting do please check out the popular science book that accompanies the program: The Undercover Scientist.

You can find more details about how the app works in the original blog entry.

Please leave a comment if you need help and I'll reply as soon as I can.

http://www.theapplelounge.com/telefonia-mobile/istethoscope-giochiamo-a- fare-i- dottori/

If any reader of the book or user of the program has any ideas for other free "undercover scientist" programs for the iphone, or something for the "Why Sh*t Happens" US version, let me know!

For fun I recently created an application for the iPhone - iStethoscope which basically turns the device into a stethoscope, allowing you to listen to your own heartbeat (or other quiet sounds nearby). I've linked it to The Undercover Scientist book, using the little scientist cartoon as a friendly way to show (hopefully interesting) facts related to sound and hearts.

For those interested, here's a little detail about how it works. The program takes audio from the microphone, buffers it for a very short amount of time and then plays it. Playing is continuous as new audio is received, so all processing has to be performed on-the-fly as the data is copied from input to output buffers. Inevitably a small delay results from this buffering process. Several types of processing happens - a low-pass filter is applied to remove hiss, a high-pass filter is applied to remove rumble, a heartrate monitor listens and attempts to count repetitive noises separated by quiet, and an automatic volume control listens for excessively loud sounds. If a loud noise is detected, the filter parameters are adjusted to reduce the volume. These adjustments are then slowly returned to normal when only quieter sounds are detected. The different modes correspond to different filter settings and different gain settings for the volume control. "Heartbeat" uses a heavy low-pass filter to let low thuds through but remove most higher- pitched sounds and reduce crackle of microphone against skin. "Conversation" uses low and high pass filters to let through middle frequencies like those transmitted by telephones. "Clear Sound" uses minimal filtering to let most of the sound through unchanged. The heartrate monitor is active in "Mute" and "Heartbeat" modes. Because it cannot use extreme filtering to make it work better (that would make it sound awful when listening) it does get a little confused if there is any crackle or noise. It only displays the pulserate when it is reasonably sure it's right, so you have to position the microphone carefully to make it work.

Simultaneously to all this on-line processing, the controls are monitored and now and again the little undercover scientist is animated in a separate concurrent thread. It's all optimized to work with as little delay as the processor can handle. But if a different program or operating system process decides to use the processor or audio, this can screw up the audio buffering and cause minor audio glitches. (If that happens the program should be restarted to reset the buffering.) The best way to improve speed and avoid problems like this would be to do all processing in the iPhone audio Digital Signal Processor instead of in software; unfortunately the API does not permit this.

The application is now freely available on iTunes, just search for "istethoscope" in the AppStore. Please leave feedback if you download it!

For details about version 1.1 click here.

For details about version 2.0 click here.

The website for the application is: http://www.peterjbentley.com/istethoscope.html