Lectrosonics Inc HMAA1 用户手册
HMa
LECTROSONICS, INC.
4
Wideband Design
The HMa transmitter uses ±75 kHz wide deviation for
an excellent signal to noise ratio and wide dynamic
range. The DSP controlled input limiter features a wide
range dual envelope design which cleanly limits input
signal peaks over 30 dB above full modulation. Switch-
ing power supplies to provide constant voltages to the
transmitter circuits from the beginning (3 Volts) to the
end (1.7 Volts) of battery life, and an ultra low noise
input ampliier for quiet operation.
an excellent signal to noise ratio and wide dynamic
range. The DSP controlled input limiter features a wide
range dual envelope design which cleanly limits input
signal peaks over 30 dB above full modulation. Switch-
ing power supplies to provide constant voltages to the
transmitter circuits from the beginning (3 Volts) to the
end (1.7 Volts) of battery life, and an ultra low noise
input ampliier for quiet operation.
Digital Hybrid Wireless
®
Technology
All wireless links suffer from channel noise to some de-
gree, and all wireless microphone systems seek to mini-
mize the impact of that noise on the desired signal. Con-
ventional analog systems use compandors for enhanced
dynamic range, at the cost of subtle artifacts (known as
“pumping” and “breathing”). Wholly digital systems defeat
the noise by sending the audio information in digital form,
at the cost of some combination of power, bandwidth and
resistance to interference.
gree, and all wireless microphone systems seek to mini-
mize the impact of that noise on the desired signal. Con-
ventional analog systems use compandors for enhanced
dynamic range, at the cost of subtle artifacts (known as
“pumping” and “breathing”). Wholly digital systems defeat
the noise by sending the audio information in digital form,
at the cost of some combination of power, bandwidth and
resistance to interference.
Lectrosonics Digital Hybrid Wireless
®
systems over-
come channel noise in a dramatically new way, digitally
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
encoding the audio in the transmitter and decoding it
in the receiver, yet still sending the encoded informa-
tion via an analog FM wireless link. This proprietary
algorithm is not a digital implementation of an analog
compandor but a technique that can be accomplished
only in the digital domain, even though the inputs and
outputs are analog.
Channel noise still impacts received signal quality and
will eventually overwhelm a receiver. Digital Hybrid
Wireless
will eventually overwhelm a receiver. Digital Hybrid
Wireless
®
simply encodes the signal to use a noisy
General Technical Description
channel as eficiently and robustly as possible, yield-
ing audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission.
ing audio performance that rivals that of wholly digital
systems, without the power and bandwidth problems
inherent in digital transmission.
Because it uses an analog FM link, Digital Hybrid
Wireless
Wireless
®
enjoys all the beneits of conventional FM
wireless systems, such as excellent range, eficient
use of RF spectrum, and resistance to interference.
However, unlike conventional FM systems, it does
away with the analog compandor and its artifacts.
use of RF spectrum, and resistance to interference.
However, unlike conventional FM systems, it does
away with the analog compandor and its artifacts.
No Pre-Emphasis/De-Emphasis
The Digital Hybrid Wireless
®
design results in a signal-to-
noise ratio high enough to preclude the need for con-
ventional pre-emphasis (HF boost) in the transmitter and
de-emphasis (HF roll-off) in the receiver. This eliminates
the potential for extreme distortion on signals with
abundant high-frequency information.
ventional pre-emphasis (HF boost) in the transmitter and
de-emphasis (HF roll-off) in the receiver. This eliminates
the potential for extreme distortion on signals with
abundant high-frequency information.
Low Frequency Roll-Off
The low frequency roll-off can be set for a 3 dB down
point at 35, 50 or 70 Hz to control subsonic and very
low frequency audio content in the audio. The actual
roll-off frequency will vary slightly depending upon the
low frequency response of the microphone.
point at 35, 50 or 70 Hz to control subsonic and very
low frequency audio content in the audio. The actual
roll-off frequency will vary slightly depending upon the
low frequency response of the microphone.
Excessive low frequency content can drive the trans-
mitter into limiting, or in the case of high level sound
systems, can even cause damage to loudspeaker
systems. The roll-off is normally adjusted by ear while
listening as the system is operating.
mitter into limiting, or in the case of high level sound
systems, can even cause damage to loudspeaker
systems. The roll-off is normally adjusted by ear while
listening as the system is operating.
Bias Voltage
42V,15V, 5V
+4V
Input
Amp
Shunt
Limiter
AUDIO
FREQ
UP
DWN
Reference
Crystal
Reference
Crystal
3 V
Battery
Hi.Lo
Pass
Filter
Filter
Digital
Pot
Audio
Level
Phantom
Power
Audio
A-D
Converter
11001001
D-A
Converter
11001001
Control P
anel
Microprocessor
Voltage
Controlled
Oscillator
Final
Amplifier
Filter
Amp
Encoded Audio
and Pilot Tone
Bicolor
Modulation
LEDs
Switching
Power
Supply
Digital Signal Processor
Phase Locked Loop
LCD
1.2V
4V
-3.3V
+3.3V