16 bit, 48 kHz format. Audio streamed to M400C is down-mixed to a single channel and played
on the mono loudspeaker. Audio captured by the microphones on M400C is processed by the
onboard DSP depending on the current audio use case and streamed to the host.
The following use cases are available:
• Playback
Direct Playback
The default playback mode. Audio sent to the sound card is played on
the loudspeaker without any processing.
• Record
Direct Record
The default record mode. Audio recorded from the front microphone is
sent to the host without any processing.
Live Record
Audio recorded by the front two microphones is sent to the host without any
processing.
Personal Record
Audio recorded by the microphones is processed by the codec DSP to
record audio coming from the direction of the user (beam forming).
The API to switch between different use cases is detailed in Section 3.2.
Table 2.2 lists the hardware configuration of the microphones, DSP features, and the stream
channel mapping per audio use case.
Microphones
DSP Features
Audio Channel
Use Case
Rear
Middle
Front
AEC
Array
Left
Right
Direct Record
Unused
Unused
Used
No
No
Front Mic
Front Mic
Live Record
Unused
Used
Used
No
No
Middle Mic
Front Mic
Personal Record
Used
Used
Unused
No
Yes
Processed
Processed
Table 2.2: Audio Use Case Details
Definitions of terms are as follows:
AEC
Active echo cancellation. Reduces feedback from speaker playback in recording.
Array
Array processing. Also known as beam-forming.
Left
Left channel of USB input stream.
Right
Right channel of USB input stream.
Processed
Multiple microphones are sampled and processed to form a single channel stream.
2.2.7
Orientation Sensor
M400C has an integrated orientation sensor with separate accelerometer, gyro, magnetometer
functions. Each function reports
(
X, Y, Z
)
values. The sensor also reports the device orienta-
tion using quaternion components
(
W, X, Y, Z
)
. The sensor readings are reported to the host
over the USB Sensor HID class. For details see Section D.3.
The orientation of the X-, Y-, and Z-axes relative to the M400C device is shown in Figure 2.1.
7
Revision 7
Vuzix Corporation
