session: audio performance, specifications & testing for hd radio audio testing graham boswell...

Session: Audio Performance, Specifications & Testing for HD Radio

Audio TestingGraham Boswell

© Copyright Prism Media Products Ltd. 2007


Prism Sound T&M - a brief history

• Prism Sound has focused on digital audio test tools since 1989– 1990: AES/EBU Channel Status analyzer in an MS- DOS ISA-bus PC– 1993: dScope “I” – dual ISA cards; AES sig gen and FFT analysis, plus DSA-1

Hand-held analyzer for interface tests– 1995: dScope “II” with improved generator and automation– 1996: DSA-1 updated to include generator with jitter simulation– 2001: dScope Series III beta. A new approach – software based instrument– 2002: dScope Series III Release 1.00– 2003: 16:2 I/O expansion switcher for dScope– 2004: Passive Low Pass Filter for Digital Amplifier measurement– 2005: dsNet-VSIO Multi-channel I2S interface for chip-level interfaces– 2005: DSA-1 system manager and remote control software for Win XP– 2006: dScope Series III software V1.20 - adds multimedia and acoustics tests


Why test?

• Maximize the basic channel performance– Before considering “optimizer” processors

• Ensure regulatory compliance

• Competitor behaviour & compliance

• Testing is a competitive weapon


Audience issues

• Cost of HD digital receivers vs service improvement

• Does the HD digital feed sound better than the analog?

• Is the digital coverage equal or better than analog?

• Is “analog only” better than the HD analog feed?

• How can we optimize HD Radio transmissions?


Broadcaster issues

• How can radio engineers help to meet business objectives?

• Are there regulatory issues?

• Competitive issues

• Audio & sound quality optimization & measurement

• Digital channel quality– At the station - digital and/or analog– Transmitter links– Listener experience

• Existing analog channel– At the station - digital and/or analog– Transmitter links– Listener experience


dScope Series III• Analog & digital signal generation

and measurement for electronic and acoustic applications

• Small, lightweight system unit

• Good RF immunity

• USB for easy hook-up to notebook

• Fast in operation

• Easy automation & data collection using host PC

• Remote operation possible using internet protocol (IP) link

• Scheduled operation also possible


dScope Series III• Makes and displays many

measurements at the same time– Example: Amplitude, Frequency,

Phase, THD+N, THD only, FFT, Harmonic analysis + AES Eye pattern

• Now provides direct generation & measurement to/from Windows sound card devices

– Allows direct measurement of sound card performance in A/D or D/A modes


DSA-1• Digital audio “connectivity” related

signal generation & measurement

• Test audio channel integrity

• Test meta-data - Channel Status

• Test AES or S/PDIF bearer quality– Fs & Data Jitter, Eye narrowing etc

• Small, lightweight, battery-operated

• Good RF immunity

• Automated test sequences built-in

• USB/serial PC option (non-essential) allows remote operation


Measurement issues

• Basic performance– Frequency response/bandwidth– Residual noise– Distortion

• Codec behaviour– Use of multitone techniques– Measurement of the channel

• Broadcast audio processors– Measurement with optimizer processor in circuit

• Digital interconnects– CODECs again– Data integrity– Meta-data


Basic audio tests

• Amplitude sensitivity

• Noise, at low signal level

• Noise & distortion at high signal level

• Frequency response


Multitone audio channel test

• Uses multi-frequency stimulus, more akin to the real world

• Measure many parameters quickly

• Great for mixed analog/digital paths and paths with data compression codecs


AES: If everyone complies

• It’s bound to work

• Pigs might fly


Introduction to AES3


Channel status


Digital audio tests: AES3

• Not all manufacturers meet every detail of the standard

• Equipment of different ages might be used

• The system designer may make errors in design of interconnections

• Problems may not show up right away – for example, only when a particular route is made

• Problems may be intermittent

• AES17 – Test Methods not well used in practice (?)– Jitter susceptibility focuses on distortion rather than clicks/errors– Does not really address problems of system installations


Some things that can go wrong

• Meta-data issues - VUCP

• Audio – Coding, Wordlength (Bit-depth), Sampling rate (CS byte 4 bit 7 !!),– Use of 2-wire (mention early DVD-A's)

• Basic frequency lock– Running unlocked can give the impression of working, but with ticks

• Carrier signal generation & transmission– Clocking/source jitter,

• Carrier signal propagation issues– Transmission line effects, impedances, eye pattern, inter-symbol interference

• Carrier signal reception & clock extraction, recovery of the data

• Conflicting interpretations– What response is appropriate if the standard is violated?


AES3 demo setup at Booth N3116

AES Out

AES ReturndScope

DSA-1


Interface and sampling jitter

Jitter on AES3 interfaces is a big problem:

• Can cause unreliable interconnection – Intermittent and hard to diagnose

• Fs and Data Jitter - A variety of manifestations– Fs Jitter – caused by the source– Data Jitter – modification of transmission waveform as a result of

transmission media characteristics

– Eye Closure – Data jitter method, program-independent

• Can cause SAMPLING JITTER– Loss of audio quality in A/D and D/A converters– Progressive and hard to diagnose


Sampling jitter example

• Two DAC’s, one with jitter attenuation– Test tone 12kHz, sinusoidal jitter 6kHz– 18-bit DAC with 56dB THD+N!


Sampling jitter example 2

• Two DAC’s, one with jitter attenuation– JTest twin-tone 12kHz & 1-bit 250Hz undithered– 18-bit DAC with 73dB THD+N, caused by cable!


Principle of fs jitter


Principle of data jitter


Data jitter in the real world


Eye Closure

• Amplitude– Wideband carrier amplitude, V P-P

• Eye Closure– In DSA-1 or dScope, worst-case Data Jitter, program independent– At zero-crossing or 200mV P-P amplitude


To the rescue

• Design-in AES3 system reliability– Systems engineers – check product specifications and check cabling

plans very carefully.

• Make it easy – AUTOMATE

• Test system components if possible– Inputs, Outputs and long cable runs

• Installation: Check for Meta-data, Audio and Carrier signal issues

• Patch/re-clock/re-generate to test the diagnosis of faults found

• Use tools that can log infrequent events for later inspection– Catch glitches, clicks etc– Monitor program transmissions non-invasively

• Run scheduled tests using a short multitone burst


Summary

• Testing can help optimize the sound of HD Radio

• Prism Sound dScope Series III– More audio test tools and better performance in a smaller, lighter package– The least cost solution for equivalent feature set

• Prism Sound DSA-1– A unique and established tool for checking AES & SPDIF connectivity

• Come and find out more at NAB 2007 Booth N3116

• Visit us at http://www.prismsound.com


Resources

• Downloads page:http://www.prismsound.com/test_measure/support_subs/support_downloads.php sub-section: "Other downloads“

• DSA-1 Manager software

• DSA-1 user Manual

• dScope Series III Software including user manual/help

• dScope Series manual PDF

• E-mail questions to:graham.boswell@ prismsound.com

session: audio performance, specifications & testing for hd radio audio testing graham boswell...

Documents

prism sound tm

hd digital feed sound

dscope series iiimakes

digital audio test tools

hd analog feed

digital coverage equal

audio performance

brief historyprism sound