presto - preservation technologies for european broadcast archives

Centro Ricerche e Innovazione Tecnologica

Presto - Preservation Technologies forEuropean Broadcast Archives

Work Package 4

Status Report


Test bed architecture

A/D Converter 24 bit@48 KHz

Player control interfaceTape/Vynil

Player

BWF

BWF

BWF

XML

XML

XML (House keeping data)

Mp3/BWF

Quality Control(acquisition monitor)

Acquisition&

Player Control

BWF

MP3 encoder

Quality Control(process monitor)

LosslessCompression

Key link 4.3Key link 4.4

Key link 4.1

Key link 4.2


WP4 workplan



key link 4.1:

QUALITY MONITOR


Audio Quality Monitor

Algorithms developed for:

computations of signal features

silence detection

bandwidth computation

click detection Algorithm under construction:

channel phase correlation


Signal Features

power: estimated through the mean square amplitude

peak level: maximum sample value

dynamic: difference between maximum and minimum

sample values

presence of DC: estimated through the mean of sample

values


Silence Detection

Robust detection of silence can be based on the comparison of values of the following parameters with properly set thresholds:

absolute energy

ratio between local and average energy

sample variance

sample maximum

For light computation, only sample variance is used.


Bandwidth Computation

The power spectral density of a function s(t), sampled at N

points to produce FFT values c0-cN-1, can be estimated

by the sum squared amplitude (SSA):

Let k the index such that:

that is, k is the index that split the total power in .

Then, the bandwidth can be estimated as (F=sample freq.):

1 ,


Click DetectionThe audio signal is modeled with autoregressive (AR) or all pole model:

According to AR model, the observed data x[t], corrupted

by clicks, is filtered using prediction error filter:

In this way the detection signal is:

The coefficients ai are estimated by the Maximum Entropy Method.


Integration into Elettra System

process monitor (on-line): all the processing functions are integrated through a library into the Elettra system:

input: buffer of data samples (size configurable)

output: log file + interface with visual tools

acquisition monitor (off-line): it is an executable program:

input: BWF file (audio 48KHz, 24bit, stereo)

output: XML file (quality analysis)


Exploitation (1)

As stated in the Key Links System Specification Document, ITC-irst will release two sets of libraries:

Video Quality Control Audio Quality Control

compiled for Linux OS, and documentation.

The packages can be exploited in the following ways:

within and beyond Presto, by all the project partners for demos of Presto results

beyond Presto, even for commercial purposes after an agreement with ITC-irst


Exploitation (2)

Usually, ITC-irst does not release source codes

exploited for commercial purposes, neither

guarantees heavy support.

More relaxed conditions are applied if exploitation

regards demos and research. However, we decide

case by case, and all the aspects of the

agreement are defined during the negotiation.



key link 4.3:

PLAYBACK DEVICE IMPROVEMENTS


Turntable improvement

Double arm for 78 RPM Two different pickups can be used at the same time:

E.g. conical vs. elliptical stylus or .0040” vs. .0028” stylusBoth output can be captured and compared in the digital

domain with the aid of Quality Control Commercial solutions are disappearing from the

marketStart/stop automation for 33 RPM

Automatic synchronisation between reproduction and capturing equipment under software control

No commercial solutions available


Activities carried out so far

Interface control document available Command set: start, stop, status Physical layer: RS232

Basic turntable components selected Plate, motor, electronics: Technics 1200 Tonearm: SME 309/312. Up to 2 arms per turntable

First prototype mechanical design completed Turntable base and arm fixing block Arm lift device Stop detector

Physical realization is under way


A/D conversion technology selection (1)

Stagetec Reference Master 24 bit quad converter tested against Apogee PSX-100 24 bit Sigma/Delta conversion unit

Extensive set of objective measurements have been carried out THD+N curves are significantly different Stagetec shows extended dynamic range, close to

theoretical values



Subjective tests (expert panel listening) Test materials:

Live recording of the RAI orchestraRecording of vynil records (33 and 78 RPM) at nominal levelRecording of vynil records at low level (30 dB below nominal)

Test set upThe listening was performed with both loudspeakers (Genelec

S30c and 1038A and Dynaudio) and with headphones (Stax Lambda Pro with diffuse field eq) using Apogee PSX-100 24 bit D/A converter for all the materials

Low level materials were played after rescaling at nominal level

5 expert listeners took part in the evaluation


Preliminary resultsThe listeners were hardly able to detect any difference on

nominal level recorded materials– Altought this could be due to the insufficient resolution of the

D/A converter, it seems that THD+N values lower then -100 dB are scarcely perceptible during normal listening

The extended dynamic range of Stagetec was clearly perceivable on low level recorded materials

Further tests will be performed by applying restoration techniques (denoise, declick) to vynil recorded materials




key link 4.4:

LOSSLESS COMPRESSION


Presto ProjectWP4 - AUDIO DIGITISATION

key link: Lossless Compression Tecnology (LCT) With Lossless Compression Tecnology is possible to

reduce the storage necessary for the digitized material

24bit - 48kHzlinear

24bit - 48kHzlinear

24bit - 48kHzcompressed

24bit - 48kHzcompressed



Any Lossless Compression Module (LCM) can be considered as a trasparent layer for the applications accessing the archive storage area

BWF format

BWF format

in

out

LCM codec Digital archive

24bit/48kHzcompressed24bit/48kHzcompressed



Software requirement: Integration in an acquisition automatic process

(command line version, etc..) algorithm robustness Public source code / Open Project Platform independence Encoding/decoding faster than real time Partial file decoding



Market survey - Main software features

Product Version Source available OS supportFLAC 1.0 yes anyLPAC 1.31 no Win/Linux

Monkey's Audio 3.92b no windows onlyPkZip 4.00 no anyRKAU 1.07 no windows only

WavPack 3.9 no windows only



Test Material

Source: 33 RPM vinyl Status: sufficient/good Material: 7 item selection from classic, jazz, rock&pop

records Total duration: about 107 minutes



Test Material

Two level test: step 1: broadcast quality @ 24 bit / 48kHzstep 2: CD quality @ 16 / bit 48kHz



Compression Ratio

0,0

10,0

20,030,0

40,0

50,0

60,0

70,080,0

90,0

100,0

24 bit 16bit

%

FLAC

LPAC

Monkey's Audio

PkZip

RKAU

WavPack

original



Compression Time Ratio (n:1)

0

5

10

15

20

25

30

35

40

24 bit 16bit

n:1

FLAC

LPAC

Monkey's Audio

PkZip

RKAU

WavPack

n:1 means n times faster than realtime



Hardware Platform

Pentium III @ 1 GHz 256 Mbyte RAM (DDR 266 MHz) OS Windows 2000

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