LA4X
Amplified Controller
user manual
VERSION 4.0
LA4X_UM_EN_4.0
w w w . l - a c o u s t i c s . c o m
10
2.2
Signal processing and amplification
2.2.1
Signal inputs
The LA4X features four input connectors allowing it to receive four analog signals, four digital signals, or two analog
and two digital signals, depending on the input mode selected by the user (see section 3.4.1). This architecture also
allows digital-to-analog or digital-to-digital fallback.
Analog inputs
The LA4X can be fed with up to four balanced analog audio signals using XLR3 female input connectors ANALOG IN A
to ANALOG IN D (see Figure 2). Each analog input port is ESD protected.
The analog input panel also features four XLR3 male link connectors passively wired to the input connectors. They
allow transmitting the input signals to daisy-chained amplified controllers. Each analog link port is ESD protected.
To be processed by the DSP, the analog signal must be converted into a digital signal. For this purpose, the LA4X
amplified controller is fitted with four cascaded 24-bit A/D converters with a sampling rate of 96 kHz allowing an
encoding dynamic range of 128 dB.
AES/EBU digital inputs
The LA4X can be fed with up to four AES/EBU digital audio signals (transported in pairs) using XLR input connectors
AES/EBU IN A&B and AES/EBU IN C&D (see Figure 2).
Each AES/EBU input port is an XLR3 female connector. The audio signals can come from a digital mixing desk or a
digital audio network bridge compliant with the AES/EBU (AES3) or coaxial S/PDIF (IEC 60958 Type II) digital audio
standards. Each AES/EBU input port is ESD protected and transformer balanced.
The AES/EBU input panel also features two XLR3 male link ports actively connected to the input ports (with failsafe
relay in case of mains absence). They allow transmitting the input signals to daisy-chained amplified controllers. Each
AES/EBU link port is ESD protected and transformer balanced.
Each AES/EBU input port is equipped with a Sample Rate Converter (SRC) that has been selected to support a wide
range of input formats (16-24 bits/ 44.1-192 kHz). It converts any of them to the 24 bits/96 kHz internal format used by
the amplified controller. The SRC is a high-quality hardware component (140 dB dynamic range, THD+N<-120 dBfs,
strong input jitter attenuation) and provides constant propagation delay regardless of the input sampling frequency.
There is no external synchronization mode. The amplified controller’s clock always runs using its high-precision internal
quartz at 96 kHz. This ensures low jitter and high audio quality in live conditions (large cable lengths, large number of
amplified controllers) while preventing phase shift, as required for line source systems
.
Digital domain benefits
Keeping the signal in the digital domain will provide the following benefits (with any digital mixing desk or any
audio network) compared to the analog signal distribution:
Better audio quality by removing one D/A - A/D cycle.
Better dynamics thanks to the digital links’ immunity to ground loops.
Optimized level chain by removing the risk of level misalignment between console and amplified controllers.
Digital signal refreshed at each amplified controller in a daisy-chain.
Improved maximum cable length. The LA4X has been tested with
up to 305 m/1000 ft
of 3 models of
AES/EBU rated cables: Belden
®
1696A, Klotz Cables
®
OT234H, and Sommer Cable
®
SC BINARY 234 (single
cuts, digital source signal running at Fs = 48 kHz).
