Meridian Audio MLP Encoder Owners manual
MLP
MLP ENCODER
USER GUIDE
Meridian MLP Encoder User Guide
i
PREFACE
Copyright and acknowledgements
Sales and service in the UK
Meridian Audio Ltd
Stonehill
Stukeley Meadows
Cambs
PE29 6EX
England
Tel (01480) 52144
Fax (01480) 459934
World Wide Web – www.meridian-audio.com
Designed and
manufactured in the UK by
Digital Gramophone and Wireless Ltd
Stukeley Meadows
Sales and service in the USA
Meridian America Inc
3800 Camp Creek Parkway
Building 2400
Suite 122
Atlanta
GA 30331
Tel (404) 344 7111
Fax (404) 346 7111
Stonehill
Cambs
PE29 6EX
England
Copyright © 1999, 2000 Digital Gramophone and Wireless Ltd.
Part no: MLP/1
The MLP software and this
documentation are copyright materials.
No part of the MLP software may be
reproduced, transmitted, transcribed,
stored in a retrieval system, or translated
into any language, or computer
language, in any form or by any means
without the prior written permission of
Meridian Audio Ltd and its licensor(s).
Additional copies of this guide may be
made and distributed provided they
include this copyright notice.
Meridian Audio Ltd and its licensor(s)
specifically retain title to all MLP
computer software. The software
described in this guide is furnished
under a license agreement and may only
be installed, used, or copied in
accordance with the terms of that
agreement.
The information in this guide is believed
to be correct as of the date of
publication. However, our policy is one
of continuous development and so the
information in this guide is subject to
change without notice, and does not
represent a commitment on the part of
Meridian Audio Ltd or its licensor(s).
Meridian and the Meridian logo are
registered trademarks of Meridian
Audio Limited. MLP is a registered
trademark of Dolby Laboratories
Licensing Corporation, in the United
States of America, and other countries.
All other brand names, product names
or trademarks belong to their respective
holders.
This guide was produced by:
Human-Computer Interface Ltd,
www.interface.co.uk
ii
Contents
Introduction 1
Overview of MLP 2
Other features 4
Making an MLP Stream for
DVD-Audio 5
Typical workflow 6
Encoding 7
Checking an encoded file 10
Using the MLP Encoder 13
Installing the Meridian MLP Encoder 14
Creating a new project 17
Specifying the input files 18
Specifying the encoding options 21
Specifying the channel assignments 23
Specifying the downmix 26
Specifying the output files 27
Specifying the checking options 28
Encoding the project 30
Checking the encoded file 32
Appendix A – Command-line
MLP Encoder 35
Command format 36
Input 38
Options 41
Channel assignment 44
Downmixing 46
Output 47
Encoding 48
iii
Appendix B – Command-line
Proofing Decoder 51
Command format 52
Options 54
Output 55
Index 57
iv
Introduction
This chapter gives an introduction to MLP, with information about its
benefits and the expected savings it achieves for different materials.
1
INTRODUCTION
Overview of MLP
Meridian Lossless Packing (MLP) is an encoding system designed to
compress high-quality digital audio data with bit-for-bit accuracy. Unlike
perceptual, or lossy data reduction, MLP guarantees not to alter the final
decoded signal in any way, but merely packs the audio data more
efficiently into a smaller data rate.
MLP encoding provides two main benefits:
•
It minimises the size of the compressed data, allowing a larger amount
of data to be stored in a given capacity.
•
It can reduce the maximum instantaneous peak data rate.
This second feature is important for DVD-Audio which has an upper limit of
9.6Mbps. Six channels of 96kHz 24-bit Linear PCM audio have a data rate of
13.824Mbps, which is well in excess of the capability of DVD-Audio. Also at
this data rate the data capacity of the disk would limit the playing time to
approximately 45 minutes. MLP encoding can reduce the worse case data
rate to 9.6Mbps, in addition to extending the playing time to the industry
norm of 74 minutes.
The following table gives examples of the typical compression that can be
achieved with different audio sample rates and wordsizes:
Format Minimum Typical
48kHz, 16-bit 0% 50%
96kHz, 20-bit 40% 55%
96kHz, 24-bit 38% 52%
192kHz, 24-bit 43% 50%
The following table gives examples of playing times on DVD-Audio that can
be obtained with different channel, sample rate, and wordsize
combinations:
Format Playing time
6 channels, 96kHz, 24-bit 86 minutes
5.1 channels, 96kHz, 24-bit 100 minutes
2 channels, 192kHz, 24-bit 2 hours
2 channels, 96kHz, 24-bit 4 hours
2 channels, 44.1kHz, 16-bit 12 hours
1 channel, 44.1kHz, 16-bit 25 hours (talking book)
2
INTRODUCTION
How it works
Because MLP was originally designed with consumer applications in mind,
one of its design aims is that any complexity must be in the encoder rather
than the decoder. The design of the decoder ensures that it will remain
lossless irrespective of the hardware platform or processor it is
implemented on. In addition, the decoder is driven by information in the
bitstream, allowing improved versions of the encoder to be developed
without becoming incompatible with the installed base of decoders.
MLP encoding uses a combination of three methods to reduce the data
rate:
•
Lossless matrixing is used to reduce the correlation between channels.
•
Lossless waveform prediction is used to reduce the inter-sample
correlation.
•
Entropy coding is used to reduce the data rate by efficiently encoding
the most likely occurring values in the audio data.
MLP does not make any assumptions about the assignment of channels, or
the correlation between channels, but takes advantage of whatever
redundancy is present in the overall signal to encode the data using the
smallest possible bandwidth.
In addition to these procedures for reducing the data rate, MLP uses stream
buffering to reduce the variations in the transmitted data rates, and absorb
transients that are hard to compress, in order to ensure a maximum
instantaneous peak data rate. The buffer allows the peak data rate to be
minimised for virtually all practical audio data.
If the audio data cannot be compressed within the specified peak data rate
the MLP Encoder will signal an error. The producer can then use one or
more options for reducing the data rate, or reducing the total space used
by the recording. These include:
•
Reducing the bit width of one or more channels, such as from 24-bit to
22-bit.
•
Filtering one channel to LFE.
•
Reducing the audio bandwidth; for example, by filtering information
above some arbitrary frequency, such as 40kHz when sampling at 96kHz.
All of these options will increase the amount of compression that MLP can
achieve, thus increasing the playing time or reducing the peak data rate.
3
INTRODUCTION
Other features
Two-channel downmix
Content providers will often want to make a two-channel version of a
multi-channel audio stream available on a DVD-Audio disk, for consumers
who only have a two-channel playback device. One option is to create
separate multi-channel and two-channel streams, and write these
separately to the disk. However, this requires two separate mastering and
authoring processes, and uses disk capacity.
MLP provides an elegant and simple solution to providing a two-channel
downmix. The encoder includes lossless matrixing, which can encode a twochannel downmix as a linear combination of the multi-channel mix and
encode this alongside the multi-channel version on the DVD-Audio disk.
The advantage of this approach is that the producer can listen to the
downmix at the encoding stage in the knowledge that it will be delivered
bit-for-bit to the end user at the decoding stage. Another advantage is that
a two-channel-only playback device does not need to decode the multichannel stream, and need only decode the stereo.
Other features
In addition to audio the MLP stream can carry hierarchical metadata, which
can include:
•
Dynamic range control data.
•
Ownership and copy protection fields.
•
Time codes.
•
Descriptive text fields.
In addition MLP has powerful built-in error detection that allows rapid
recovery from bit-stream errors, and prevents any erroneous noises, clicks,
or bangs following data errors.
4
Making an MLP Stream for DVD-Audio
This chapter describes the workflow of an MLP encoding project for
DVD-Audio using the Windows-based MLP Encoder, together with the
MLP command-line tools described in subsequent chapters of this
guide.
5
MAKING AN MLP
STREAM FOR DVD-
AUDIO
Typical workflow
The following diagram shows a typical workflow from the input audio files
through to the output MLP file:
Input files
Encoding
MLP Encoder
DVD Audio
WAV AIFF
Compression options:
Sample rate
Word size
Channel assignments
Windows
mastering
Log
file
Sonic Solutions
Soundfiles
MULTIWAV
MLP Encoder
MLP_ENC
DVD-Audio
LPCM
Downmix options:
Matrix coefficients
MLP
file
Proofing decoder
MLPPROOF
Downmix
Log
file
WAV
file
MIXNULL
WAV
file
Listening
tests
The different sections of this workflow are explained in greater detail in
the following sections, and in the PDF files on the installation disk.
6
MAKING AN MLP
STREAM FOR DVD-
AUDIO
Encoding
Input files
The MLP Encoder processes audio data from one or more input file. The
MLP Encoder directly supports WAV, AIFF, and LPCM (uniform-rate) audio
formats, and in addition the command-line version supports raw binary.
Files in Sonic Solutions soundfile format, or DVD-Audio LPCM mixed-rate
format, can be converted into WAV format for use with the MLP Encoder
using the command-line tools MULTIWAV and DVDWAV respectively.
MLP Encoder
The MLP Encoder is an intuitive Windows-based program that simplifies the
steps involved in encoding a set of one or more audio files, and then
checking the resulting MLP file.
To use the MLP Encoder the following options need to be specified:
Sample rate and wordsize
The sample rate and wordsize will be set to the corresponding values in the
input files.
Channel order and assignments
DVD-Audio supports up to six channels in one of 21 alternative channel
assignments.
To run the MLP Encoder you need to specify the channel assignment, and
the location of each of the channels in the source files.
7
MAKING AN MLP
STREAM FOR DVD-
AUDIO
DVD-Audio channel assignments
Channel
Assign
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Ch 0
M
L
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Lf
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5
R
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
Rf
S
Ls
LFE
LFE
LFE
Ls
Ls
Ls
Group 1 Group 2
Rs
Ls Rs
C
C
Ls
C
LFE
C
LFE
C
LFE Ls Rs
C
C
Ls
C
LFE
C
LFE S
C
LFE
C
Rs
Rs
Rs C LFE
S
S
S
Rs
S
Rs
Ls Rs
LFE
C
Number in
Group 1
Number in
Group 2
10
20
21
22
21
22
23
21
22
23
22
23
24
31
32
31
32
33
41
41
42
M MonoKey:
L Stereo Left
R Stereo Right
Lf Left front
Rf Right front
C Centre
LFE Low Frequency Effects
S Surround
Ls Left surround
Rs Right surround
Channel groups
The channel assignments group the channels into two groups, referred to
as Group 1 and Group 2. The significance of the group is that the sample
rates and wordsize can be specified independently for each group. See
DVD-Audio channel assignments, above.
The DVD-Audio channel assignments 8 to 12 are almost identical to the
channel assignments 13 to 17, and differ only in the way the channels are
grouped. For these channel assignments you therefore might want to
specify whether the number of channels in Group 1 is 2 or 3 in order to
uniquely identify the channel assignment. If this is not specified the
encoder will place as many channels as possible into Group 1.
Restart gap
A restart gap of between 8 and 32 can be specified to control the overhead
of the MLP stream. The lowest, default setting of 8 allows a restart every
7ms, and this setting gives the fastest start up in cueing and the fastest
recovery from a disk error. Selecting the highest permitted value of 32 will
increase the apparent disk capacity, but increase the recovery/cue time to
27ms.
8
MAKING AN MLP
STREAM FOR DVD-
AUDIO
Pre-audio gap
To allow players or downstream decoders to lock onto the MLP stream it is
recommended that you include a one-second period of silence or irrelevant
audio (eg ambient noise) at the start of each track.
Downmix
To encode a downmix from the input channels you need to specify the
downmix coefficients to the encoder. Normally this will be done by
listening to a suitable mix on an audio workstation, and then reading the
fader settings. The command-line version of the MLP Encoder requires the
matrix coefficients to be specified as decimal fractions, and the following
table is provided to convert from dB values:
dB +6 +3 0 -3 -6 -9 -12 -15 -18 -21 -24 -∞
Coefficient 2.00 1.41 1.00 0.71 0.50 0.35 0.25 0.18 0.13 0.09 0.06 0.00
The Windows MLP Encoder automatically converts from dB values.
Downmix coefficients can range from +2 (ie +6dB) to 0 (ie infinite
attenuation), and from -2 to 0 for negative phase, where 1 corresponds to
0dB.
The downmix process does not prevent overload (clipping) of the stereo
output signal, because that may be the artistic intent. When overload
occurs, the signal is not clipped in the multi-channel MLP stream (which
continues to operate losslessly) but in the player. You can detect an output
clip using the Proofing Decoder, MLPPROOF.
9
MAKING AN MLP
STREAM FOR DVD-
AUDIO
Checking an encoded file
It is strongly recommended that all encoded files be checked carefully with
the tools provided before proceeding to author them onto a DVD. The
following sequence of checks is recommended:
• Check the encoder log file for any error reports.
• Decode the encoded file using MLPPROOF and check its log file for
errors.
• Check downmixes by creating a decoded stereo WAV file of the
downmix.
• Listen to the decoded audio files.
Logging and reporting
The MLP Encoder and Proofing Decoder each produce log files to confirm
the options that have been specified, and report error messages. In the
Windows MLP Encoder the log files are displayed in the Progress dialogue
box so that any errors can be identified, as well as being saved to disk for
later reference.
MLP Encoder log
If the MLP Encoder session has been successful the last line of the encoder
log should display:
Encoding completed
If this line is missing do not proceed to decode. Check your input material is
correctly formatted (eg view it in an editor or play it back), or re-run the
encoding as an isolated process so that the error messages on the console
can be seen.
The MLP Encoder log also displays the average bits/sample achieved by
encoding.
Checking Proofing Decoder logs
The Proofing Decoder log will end with the line
PASS
if the stream is correct. Other useful information is also included in the log,
including an alert if a downmix will clip in the player, and confirmation of
the actual channel assignment, sample rates, wordsizes, and grouping.
10
MAKING AN MLP
STREAM FOR DVD-
AUDIO
MLP file playing time
The MLP encoding process extends the audio sample by up to 1ms of
silence. The exact duration is displayed in the log for use in subsequent
authoring.
Listening tests
Listening tests are important in case the source file format was incorrect.
Checking downmixes
It is strongly recommended that all downmixes are checked using the
following procedure:
• Use the Proofing Decoder MLPPROOF to create a WAV file of the
downmix from the MLP Stream.
• Listen to the downmix and confirm it is correct.
• Check the downmix file for errors using MIXNULL.
11
MAKING AN MLP
STREAM FOR DVD-
AUDIO
12
Using the MLP Encoder
The Meridian MLP Encoder program provides a convenient Windows
interface to the MLP tools to simplify the creation of MLP streams for
DVD-Audio.
This chapter explains how to install the Meridian MLP Encoder, and
use it to create and check MLP streams.
13
USING THE MLP
ENCODER
Installing the Meridian MLP Encoder
Requirements
To use the Meridian MLP Encoder, and its associated tools, you need:
•
A computer running Windows 95, 98, NT 4 or 2000.
•
A 100MHz or faster Pentium-class processor.
•
At least 16Mbytes of RAM.
•
5Mbytes of free disk space.
The graphical user interface requires a mouse or similar pointing device – it
cannot be operated solely from the keyboard.
In addition, you must have sufficient free disk space for:
•
The input audio you intend to encode.
•
The resulting MLP file.
•
Any downmix auditioning and null-checking files you wish to generate;
see Specifying the checking options, page 28.
If encoding speed is important to you, it is strongly recommended that you
fit 128Mbytes of RAM and use a disk drive or network capable of delivering
at least 5Mbytes per second.
As a rough guide, the encoder should run at between 1 and 2 kilobytes of
input data per second per megahertz of Pentium II or III CPU speed,
depending on circumstances.
To install the Meridian MLP Encoder
• Insert the Meridian MLP Encoder CD-ROM.
• Follow the instructions on the Installation Sheet included in the
package.
14
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