Crown Audio IQ P.I.P.-DSP manual Technical Information, Audio Signals, Reference Manual

IQ–P.I.P.–DSPProgrammable Input Processor with DSP for IQ Systems

5 Technical Information

The purpose of the IQ–P.I.P.–DSPis to provide extensive signal processing capabilities and to enable an IQ System to control and monitor a P.I.P.-compatible amplifier. See Sections 2 and 3 for a list of the facilities and features. Figures 5.1 and 5.2 show hardware and signal flow block diagrams of the unit.

5.1 Audio Signals

5.1.1 Hardware Processing (see Figure 5.1)

Balanced and unbalanced audio signals enter the mod- ule at the XLR connectors. From these connectors, the signals are RFI filtered and fed into a balanced to single- ended conversion stage. Then they are sent to a monitor input (discussed below) and also to a DCA (Digitally Con- trolled Attenuator) for gain ranging via the IQ System. This is essential because the DSP (Digital Signal Processing) system has limited voltage headroom.

After the DCA, both channels are sent to an 18-bit dual- channel ADC (Analog to Digital Converter). The ADC pro- vides brick-wall low-pass filtering and “volts to bits” conversion. The output of the ADC is a multiplexed serial bitstream which is sent to the DSP. The DSP operates on each sample of both channels (one at a time) via machine language program instructions (firmware). The output of the DSP is a serial bitstream which is sent to the DAC (Digital to Analog Converter). The DAC is an 18-bit dual- channel device which demultiplexes Channel 1 and 2 and

converts the bits to volts. The DAC also provides low-pass filtering. The output of the DAC drives the amplifier inputs via the P.I.P. edge card connector as well as the “daisy chain” outputs.

5.1.2 Signal Flow Processing (see Figure 5.2)

The audio signals are attenuated via the input attenua- tors, providing system gain setting as well as gain rang- ing for the DSP system. The input compressor/limiters then allow dynamic scaling of signals for many applica- tions via common parameters such as threshold, ratio, etc. The ODEP conservation limiters then provide system protection with dynamic (but slowly varying) gain scaling based on thermal conditions within the amplifier. Next the signals are fed to the input protection limiters to keep the signal below the voltage headroom of the DSP system.

The signal is then fed into eight cascaded fully program- mable 2nd-order DSP filter cells. All filter cells are IIR based to provide a proper magnitude/phase relationship for crossover and equalization applications. Each filter cell is controllable. 1st and 2nd-order filter types use one filter cell. 3rd and 4th-order filter types use two filter cells. The output of the filter block is sent to an adjustable digital signal delay section for audio signal delay. The minimum delay is hardware-limited to 1.25 milliseconds. The output of the delay section is sent to the output limiter section. The DSP output limiter dynamically adjusts the system gain to explicitly limit the output voltage of the amplifier within ½ dB by utilizing the output voltage monitor infor- mation from the data acquisition system. Common limiter

STATUS

MONITOR INPUTS

AUDIO

MONITOR

INPUTS

CH 1

AUDIO

INPUTS

CH 2

CH 1

AMPLIFIER OUTPUTS

CH 2

SWITCHABLE INPUT PAD

SWITCHABLE INPUT PAD

PEAK

DETECTOR

PEAK
DETECTOR	AUDIO		LOG AMP
	MONITOR
PEAK	MULTI-
	PLEXER
DETECTOR
PEAK
DETECTOR
		EXTERNAL
			RESET

FUTURE HDWR IOC Vcc	ODEP
		IQ ADDRESS
		SWITCH
INPUT MUX		AMP REMOTE
A/D CONV.		STANDBY
		ISO. INPUT	CROWN BUS
			SERIAL
MICROCONTROLLER		RECEIVER
			DATA INPUT

DSPI

DROP-OUT

RELAY

CH 1

DIGITALLY

ANALOG TO

OUTPUT

DRIVER

DIGITAL DIGITAL TO

CROWN BUS

SERIAL

DATA OUTPUT

BALANCED

DAISY-CHAIN

OUTPUT

CH 1

CONTROLLED

BALANCED AUDIO INPUTSDIGITAL 2-CHANNEL

SIGNAL ANALOG

TO AMPLIFIER AUDIO INPUTS

ATTENUATOR

CH 2
		P.I.P.
EXTERNAL POWER
	POWER
SUPPLY INPUT
	SUPPLY

CONVERTER

PROCESSOR CONVERTER

EXTERNAL

MEMORY

CH 2

BALANCED DAISY-CHAIN

OUTPUT

Fig. 5.1 IQ–P.I.P.–DSP Hardware Circuit Block Diagram

Reference Manual Page 21