A user who is not familiar with the MAF file format can simply view the header

A user who is not familiar with the maf file format

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parentheses, a spacer consisting of periods, and the field description. A user who is not familiar with the MAF file format can simply view the header and use standard file I/O functions (such as fscanf in C) to load the array data into his program. While a simple program can be written in any language to load an 22
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Figure 3.3 The Megamike’s channel meters. Channels 9 through 14 are clipping. MAF file, it is most commonly loaded into MATLAB using a script provided by the author. MAF files can also be loaded back into the recorder application for quick viewing or playback through the Meagmike’s loudspeaker. Also shown by Figure 3.2, is a window in the lower-right corner of the screen, which is named, Left Play-buffer: "hfs1.dat" . The plot in this window represents a signal that has been loaded from the file named “hfs1.dat” into the Megamike’s play-buffer . By selecting Record-Play from the Recorder menu, the signal in the play-buffer is played through a loudspeaker (shown in lower left of Figure 3.1) as the signals from the microphone array are simultaneously recorded. There are two play buffers, right and left, allowing up to 2 signals to be loaded and played during a recording. Currently, only one play-buffer output is connected to an amplifier, which powers the loudspeaker. The volume of the amplifier is easily adjusted using the Megamike’s channels meters , which are shown in Figure 3.3. The meters register the power, in dB, of the signal from each microphone channel. When the meters are activated, the play-buffer signal is played through the loudspeaker in a continuous loop allowing the volume to be adjusted while the user watches the meters. If any of the meters reaches it’s maximum, which is marked by a red bar at the top of the meter, then the corresponding analog-to-digital converters (ADC) is clipping and the volume of the source must be reduced. These play-record and volume-adjustment features allow known source signals to be acquired using the full dynamic range of the array’s A/Ds. Other features of the Megamike Recorder include an adjustable countdown before recording, microphone scanning to listen for problematic microphone channels, an external trigger that is asserted at 23
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Figure 3.4 A picture of the conference room. the start of each recording, and PC-Megamike interface diagnostics. As shown in Figure 3.2, a status window, which is located in the lower-left corner of the screen, displays messages in response to the commands given to the Megamike. 3.2 The Conference-Room data set Recordings were made in a small conference room at Brown University, which is shown in Figure 3.4, using a 15-element microphone array and the Megamike Recorder . The Record-Play feature was used to play prerecorded speech through a loudspeaker while simultaneously recording the signals from the array. The use of the loudspeaker was preferable to an actual talker since the loudspeaker could be precisely located and would be fixed over the duration of the recordings. The prerecorded speech was taken from the LEMS speech-recognizer database [80] [42] [52] [67] [43], which is composed of digital recordings from a close-talking microphone worn by talkers uttering alpha-digits. Three array recordings, ranging in duration 24
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