SoundField ST250 microphone captures everyday sounds for the Beltone AVE.(tm) System. Heading the recording team, (left to right) Bruno Strapko, Strapko Recorders; Jennifer Robinson, MS, CCC-A and Greg Olsen, Project Manager, both of GN Resound, NA. SOUNDFIELD ST250 MICROPHONE PROVIDES REALISTIC 3-D SOUND FILES FOR BELTONE'S HEARING INSTRUMENT FITTING SOFTWARE CHICAGO, ILLINOIS: Times have changed for hearing instruments. Twenty-first century PC and DSP technology have replaced the screwdriver for adjusting each instrument's response to better tailor it for each individual user. Beltone Electronics, a leading provider of hearing instruments, and a pioneer in developing DSP technology for this application, enhanced its SelectaFit fitting software with realistic, calibrated, 3-D sound files recorded in the field using the SoundField ST250 microphone. As part of SelectaFit, Beltone's unique Audio Verification Environment, AVE.(TM) (pronounced "avenue"), provides a surround sound playback environment at the hearing instrument specialist's office, where a patient can listen to recordings of real-world sounds in addition to standard audiological tones and stimuli, all stored as sound files on a PC. The AVE. module and its sound field files are but one part of the total fitting protocol. "Our goal is to provide realistic expectations to the people wearing hearing instruments, of the acoustic environments they will encounter," said Greg Olsen, project manager, Fitting Systems Group, GN ReSound (owner of Beltone). Olsen said that the first attempts at creating multi-channel Dolby Pro Logic(TM) sound files used typical multiple microphone techniques and post-production effects to produce impressive sounding cinema-type surround soundtracks. The problem was these didn't sound realistic to those being fitted with hearing instruments. "Patients would say that their kitchen didn't sound like that [on the sound file]," Olsen said. A more accurate approach was needed. Enter recording engineer, Bruno Strapko, C.A.S., owner of Strapko Recorders of Schaumburg, Illinois, outside of Chicago. Strapko felt the SoundField ST250 would be the perfect mic to capture the acoustic realism of the scenes played out at different venues - a car, a pharmacy, a church, an office, a baseball game, a kitchen, a coffee shop, and a child's birthday party - typical of the variety of acoustic environments that a hearing instrument user would encounter. The scenes featured professional voice talent plus other sounds typical of the environment, like background noise, water running in the kitchen, an organ at the church wedding, and construction noise outside the car. "Our technique was simple," Strapko explained. The ST250 mic was positioned where the hearing-assisted person would be situated in the scene, and was, in effect, substitute "ears" for that person. The SoundField ST250 mic contains four capsules mounted in a tetrahedral array. Connected to an accompanying SoundField processor/preamp, the array can be configured as stereo variable-angle omni, stereo cardioid, or stereo figure eight. In place of stereo, the processor can provide "B Format" outputs, which are signals from the three dimensions (front to back, left to right, and up and down) plus a point source reference channel. Strapko recorded the scenes in both stereo and B format modes on either a Zaxcom Deva (when portable battery operation was required) or on a Mackie MDR2496 Recorder (for fixed locations). Strapko noted that most of the material was used as recorded, with simple edits on Sonic Solutions to include the correct takes. "In a few instances, we needed to go back on location to record additional elements. Again, I used the ST250 and then added it into the mix," he said. The final mix was encoded with Dolby Pro Logic and converted to a .WAV file, with lossless compression, for use in the Beltone AVE. module. Strapko said he hopes to use the ST250 mic with the new SoundField 451 processor with 5.1 outputs for future recordings that could be encoded with Dolby AC-3. "We're putting it through critical testing right now," he said. The 3-D sound files have proven very effective in the fitting suite. "There has been a great response to this," Olsen reported. "We've seen patients become very emotional when they are able to hear all of the wonderful sounds we're able to provide - many sounds they haven't heard in years." In the fitting suite, a patient listens to the sound field recordings originating from the specialist's computer through a Pro Logic decoder into a turnkey Boston Acoustics four-channel surround loudspeaker system (left, center, right, mono surround), enhanced by a subwoofer. The patient sits in the "sweet spot" surrounded by the loudspeakers that have been carefully calibrated, through the software, for proper level and frequency response. The fitting rooms are also acoustically treated to ensure playback accuracy. The Beltone SelectaFit fitting software with AVE. module is a major leap forward for hearing instrument specialists who previously had to use such non-standard sources as their own voice or jiggled keys to try to assess how well the hearing instrument was adjusted. Now the adjustments are made easily and interactively, even during the sound file playback, until the patient is satisfied with the sound level and quality of his or her rejuvenated sound perception experience. |
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