As a part of Project54, we have a newly formed Radio Testing Lab which is used for performing tests on projects related to the usage of Land Mobile Radios. Currently we are working on two projects that attempt to solve problems associated with the utilization of mobile radios. While the first project provides a solution for the interoperability problem using radio patching, the second project is based on the implementation of APCO Project 25 radio standard.

In the lab, for test equipment, we have more than fifteen radios made by different manufacturers (Motorola, Kenwood, and E. F. Jonson), several digital phosphor oscilloscopes (Tektronix TDS3000B series), a vector signal analyzer (Agilent 89441A with RF section), and a bunch of PCs and laptops. With this equipment and our experience we can assure that our projects are well tested and verified. Below are two pictures from the lab.

Using the radio patching method, we have developed a solution for the radio interoperability problem. It is based on more affordable off-the-shelf devices and represents an adequate solution for small public agencies. The system supports full radio patching with proper PTT functioning and has audio signal latency bellow what is specified by ITU-T standard. It turned out that radio patching is the cheapest and fastest solution to the radio interoperability problem. More information about the system can be found in this technical report, and here about its precursor system.

Project 25 seems a perfect solution to constant growing needs for data communications in cruisers because it supports both data and voice transmissions over radio channels. Also, most public safety agencies already have and use Project 25 compliant radios. However, in order to fully utilize their radios and Project 25 data capabilities those agencies have to purchase very expensive Project 25 data capable base stations. Small public safety agencies usually cannot afford such expensive pieces of equipment. To address this problem, we have developed a software-based Project 25 data base station as an affordable way for small agencies to bring the data into their cruisers. The project is in its final testing stage and very soon will be ready for deployment. You can read more about our base station in this previous post. More technical information about the implementation of the transmission side can be found in Eric’s thesis.

Ivan Elhart

Sony revealed an egg-shaped digital music player named Rolly (picture below) at the end of 2007, but I haven’t had the chance to see it until last weekend. It plays MP3 and AAC music files and supports direct music streaming over a Bluetooth connection. And it is able to dance.

The Rolly is more than an ordinary music player. Thus, it is motion-controlled robot with a bunch of sensors, color lights, and two flapping wings. It uses two wheels that surround the body to roll, wiggle, and spin. In vertical position the wheels can be used to change songs and adjust volume. The Rolly creates motion automatically by analyzing the music, so it can dance to any song. Also, there is a possibility of creating new motions or customizing exiting ones using PC software. You can see the Rolly’s dance in the video below. It is amazing how the sound and motion are synchronized.

Ivan Elhart

Yesterday I attended the College of Engineering and Physical Sciences Frontiers Lecture by UNH Math Professor Kevin Short, entitled “Disassembly, Repair and Rebuilding of Music using Mathematics.” As the title suggests, Kevin discussed his work on restoring old music recordings, including his Grammy Award-winning work on restoring an old Woody Guthrie recording. Kevin won his Grammy in collaboration with Nora Guthrie, Jorge Mateus, Steve Rosenthal, Jamie Howarth and Warren Russel-Smith. Jamie Howarth has a special place in this group as the founder of Plangent Processes, a pioneering company in the field of music repair.

The talk was excellent. Kevin introduced several complicated digital signal processing ideas and made them accessible to us all. In this post I will concentrate on only one topic from the talk - Kevin’s work on the Woody Guthrie recording.

When I first heard about Kevin’s work on restoring old music recordings I also heard the term wire recording, but never followed up on what it really meant. Well, it turns out that wire recording is a technique that magnetizes a steel wire to record sound. This technology was used to create the Woody Guthrie recording and, as you can imagine, it’s a challenge to get a 50 year old coil of steel wire to reproduce sound with any reasonable quality.

One problem with a wire recording has to do with the uneven speed of motion of the wire under the recording head during recording (all recording techniques that use moving parts have this problem to some extent). The uneven speed of the recording medium stretches out some sound segments in time, and it compresses others. Another problem is that handling of the medium may damage that medium, and this in turn results in similar stretching and compression of the sound in time. An extreme case of this latter problem is a cassette player chewing up your tape. The tape may still be playable but the sound it produces isn’t that great any more.

The Woody Guthrie recording suffered from this type of stretching and compression. However, Kevin and Jamie Howarth were able to restore the recording by taking advantage of a particular type of noise in the recording: powerline hum. You see, the wire recorder was plugged into a wall outlet, which provided AC current at a frequency of 60 Hz, and this frequency was pretty constant. The recording was contaminated with a 60 Hz sinusoidal noise that originated from the powerline. However, when you play back the wire recording, the frequency of this noise sinusoid fluctuates. Kevin and Jamie realized that they had a known source in the 60 Hz powerline and that, by observing the fluctuations of the frequency of the noise sinusoid on the wire, they could understand how all the other sounds were distorted as well. This knowledge can then be used to reverse the distortions (compress stretched out parts of the recording, and stretch out compressed ones). What an elegant idea!

Thanks for the excellent lecture Kevin, and thanks to the CEPS Dean, Joe Klewicki for sponsoring the lecture series. For more pictures from the even click here.

Andrew Kun