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appendix e
DSP-Induced Delays in Mixing
This appendix provides an overview of DSP-induced delays, and explains how you can compensate for these delays to improve time and phase alignment of audio in complex or critical mixing situations.
• To learn about DSP-induced delays and when
you should compensate, see “Introduction to
DSP-Induced Delay” on page 115.
• To learn how to compensate for delays automatically with Delay Compensation
(Pro Tools HD only), see “Delay Compensation” on page 116.
• To learn how to compensate for delays manu-
ally, see “Manually Compensating for Delays” on page 117.
• For details on the sources of DSP-induced de-
lay, see “Delay Factors” on page 119.
Introduction to DSP-Induced
Delay
In all digital systems, DSP processing causes signal delays of varying amounts. These DSP-induced delays can vary from as short as several microseconds to as long as several milliseconds, depending on the type of processing or routing being performed.
Do not confuse signal processing-induced delays with time domain effects processing
(such as delay, echo, reverb, and other desirable delay effects).
Each plug-in, hardware insert, and mixer assignment on a track delays that track by an amount equal to the total of all DSP-delay factors. (For
details on these delays, see “Delay Factors” on page 119.)
In some cases, signal processing delays matter only if you use a real-time TDM plug-in on one channel of a stereo or multichannel signal but not the others. This imparts an unequal amount of delay to the signals on that channel, which subsequently may cause undesirable cancellation of certain frequencies.
Audible symptoms of phase issues include comb-filtering and loss of high frequencies.
Appendix E: DSP-Induced Delays in Mixing 115
In simple terms, DSP-induced delay can cause audio to arrive at the main output (or a submix output) at different times. To maintain time alignment, you can compensate for DSP-induced delays.
When to Compensate
You may only really need to compensate for delays between tracks where phase coherency must be maintained (as with instruments recorded with multiple microphones or stereo pairs). If you are working with mono signals, and the accumulated delays are small (just a few samples, for example), you probably do not need to worry about compensating for delays.
However, larger sessions with higher track and voice counts, many plug-ins, and/or complex mixer routing can benefit when DSP-induced delays are compensated to maintain proper time alignment.
In any session, if you want to maintain absolute time alignment across all tracks you should always compensate for signal processing delays.
• You can manually compensate for delays with one or more of the following methods:
• Apply sample-level delay to tracks with the
TimeAdjuster plug-in (see “Using TimeAdjuster TDM Plug-In” on page 118).
• Manually nudge tracks earlier or later in
time as needed “Nudging Audio Tracks” on page 119.
• Use the same plug-ins on all tracks.
While learning about how to compensate for delays, keep in mind that the best results can be often obtained by using a combination of one or more methods. Doing so gives you more options for managing DSP resources as needed by Delay
Compensation and the TimeAdjuster (TDM) plug-in. In addition, the variety of tools available for compensating for delays help ensure compatibility if the session is to be transferred to another system.
Automatically Compensating for Delays
If you want Pro Tools to automatically compensate for offsets incurred by processing delays, use Delay Compensation.
How to Compensate
Pro Tools systems provide tools to compensate for signal processing delays, as follows:
• You can automatically calculate and compensate for processing delays by using the
Pro Tools Delay Compensation feature. See
“Delay Compensation” on page 116.
Delay Compensation
Delay Compensation automatically manages
DSP delays that occur on audio tracks, Auxiliary
Inputs, or Master Faders because of plug-in use and mixer routing. With Delay Compensation enabled, Pro Tools maintains time-alignment between tracks that have plug-ins with differing
DSP delays, tracks with different mixing paths, tracks that are split off and recombined within the mixer, and tracks with hardware inserts.
116 Pro Tools|HD Getting Started Guide
To maintain time alignment, Pro Tools adds the exact amount of delay to each track necessary to make that particular track’s delay equal to the delay of the track that has the longest delay.
Delay Compensation should be enabled during mixing and playback for optimal delay-compensated sound. In some cases when recording, Delay Compensation should be turned off.
For more information on using Delay Compensation, see the Pro Tools Reference
Guide.
To use Delay Compensation to compensate for
DSP-induced delays:
1 Choose Setup > Playback Engine, and choose
a Delay Compensation setting (see “TimeAdjuster and Delay Compensation” on page 117).
2 Select View > Mix Window > Delay Compensation.
3 Choose Options > Delay Compensation.
4 Use the track Delay Compensation displays and other settings to do any of the following, as needed:
• Define specific delay values for hardware inserts
• Bypass Delay Compensation per track
• Fine tune Delay Compensation for each track by entering a User Offset
TimeAdjuster and Delay Compensation
TimeAdjuster plug-ins behave in a special way when used with Delay Compensation, as follows:
• When Delay Compensation is enabled, Time-
Adjuster does not report to Pro Tools its Delay setting (the amount of delay to be added to the signal path). However, TimeAdjuster does reports its internal plug-in delay of 4 samples to Pro Tools, and this delay is reported in the track Channel Delay indicator (or Delay Compensation View) in the Mix window.
• When Delay Compensation is turned off or unavailable, TimeAdjuster operates as expected and applies its Delay setting to the
track. For more information, see “Manually
Compensating for Delays” on page 117.
This ability to maintain TimeAdjuster instances and their Delay settings lets you more easily transfer sessions between systems with and without Delay Compensation.
Manually Compensating for
Delays
If you want to manually compensate for offsets incurred by processing delays, do any of the following:
• Use the same plug-ins on all tracks.
• Apply sample-level delay to tracks with the
TimeAdjuster plug-in. See “Using TimeAdjuster TDM Plug-In” on page 118.
• Physically adjust audio tracks in the Edit window by the appropriate number of samples (for example, by using the Nudge func-
tion). See “Nudging Audio Tracks” on page 119.
Appendix E: DSP-Induced Delays in Mixing 117
Using TimeAdjuster TDM Plug-In
You can use the TimeAdjuster TDM plug-in provided with your Pro Tools system to apply an exact number of samples of delay to the signal path of the tracks you are working with. Up to
2048 samples of delay are available.
The Channel Delay indicator (dly) in the Mix window displays the total delay, in samples, incurred on a track from the use of any plug-in on that channel. TimeAdjuster can be used to match these delay values for other tracks that need to remain in phase (as can occur with instruments recorded with multiple microphones or stereo pairs, if the tracks do not use the same plug-ins).
See also “TimeAdjuster and Delay Compensation” on page 117.
For information on delay indication when using Delay Compensation, see the
Pro Tools Reference Guide.
To use TimeAdjuster to compensate for a time delay (for example, between two tracks):
1 In the Mix window, Control-click (Windows) or Command-click (Macintosh) the first track’s
Volume/Peak/Channel Delay indicator to toggle to Channel Delay (dly).
2 Note the Delay value, shown in samples.
3 Insert the TimeAdjuster plug-in on the second track (the one whose delay you want to change to match the first track).
4 Control-click (Windows) or Command-click
(Macintosh) the track’s Volume/Peak/Channel
Delay indicator until the Channel Delay (dly) value is displayed for that track.
5 Change the delay time in TimeAdjuster by moving the Delay slider or entering a value in the Delay field, until the second track’s delay value matches that of the first track.
Testing TimeAdjuster
You can test the delay values by duplicating an audio track and reversing its phase while compensating for delay.
Using TimeAdjuster with Plug-Ins
If you are using a plug-in whose delay factor you are not familiar with, you can set the delay by ear.
To use TimeAdjuster to compensate for plug-ins with unknown time delays:
• If you are working with phase-coherent track pairs, or tracks that had been multi-miked, you can “null out” the delay. Invert the phase of the target track using the TimeAdjuster
Phase Invert button, and adjust the plug-in delay time until the signal disappears. (When they are perfectly synchronized, duplicate signals of opposite polarity cancel each other out.) When you are finished, disengage the
Phase Invert button.
– or –
• Change the delay while listening to the signal in phase, adjusting until any comb-filter effects cancel out.
118 Pro Tools|HD Getting Started Guide
Nudging Audio Tracks
On audio tracks, you can use the Pro Tools
Nudge feature to nudge the affected regions in single-sample (or other) increments, to preserve phase coherency. If it is necessary to nudge a region by a large number of samples, you may want to calculate the equivalent value in milliseconds and nudge the Region in millisecond increments. If the value does not divide evenly, you can switch the Nudge value back to samples and use these smaller increments for the remainder.
The disadvantage of using this method is that it only works with audio tracks (not live inputs), and the timing relationship between tracks is permanently altered, which can affect editing.
Sample Rate and How it Affects Delay
The delay in samples caused by TDM processing is the same regardless of the sample rate because a sample is tied to the rate of the sample clock for the entire system. However, when samples are converted into a time value (milliseconds or microseconds), the sample rate (44.1 versus
48 kHz) must be taken into account.
Delay Factors
With Pro Tools HD, delay is incurred when you perform the following processes:
• Bouncing tracks. See “Bouncing Tracks” on page 119.
• Real-time processing with plug-in inserts.
See “Using Plug-In Inserts” on page 119.
• Mixing and routing with sends. See “Using
• Mixing and routing with hardware I/O
(sends or inserts). “Using Hardware I/O” on page 120.
Bouncing Tracks
Bouncing to tracks causes additional delay, as follows:
Bus-Based Bounces When you bus a track to another track and record the result, the following delays are incurred:
Bus-based bounce delays for each Pro Tools system
HD Mixer Delay
Stereo Mixer 10 samples
Surround Mixer 8 samples
Bounce to Disk The File > Bounce to > Disk command causes no delay on Pro Tools|HD systems, because delay compensation for the bounce function is built in. This form of bouncing may be more desirable than bus-based bouncing. For more information, see the Pro Tools Reference
Guide.
Using Plug-In Inserts
Using plug-in inserts on a track causes additional delay.
For specific information on the delay amounts for DigiRack or Digidesign plugins, refer to your DigiRack Plug-Ins Guide or
Digidesign Plug-Ins Guide.
Channel Delay Indicator
On all systems, the Channel Delay indicator
(dly) in the Mix window displays the total delay, in samples, incurred on the track from the use of any TDM plug-ins on that channel.
For information on delay indication when using Delay Compensation, see the
Pro Tools Reference Guide.
Appendix E: DSP-Induced Delays in Mixing 119
To see the amount of processing delay on a track that uses plug-in inserts:
â–
In the Mix window, Control-click (Windows) or Command-click (Macintosh) the track’s Volume indicator to toggle between Volume
(“vol”), Peak (“pk”) and Channel Delay (“dly”) indications.
Using Sends
When you send a track to another track and return it to a track (audio, Auxiliary Input, or Master Fader), the following delays are incurred:
Sends delays for Pro Tools|HD systems
HD Mixer
Stereo Mixer
Surround
Mixer
Sends Delay
Pre-fader send to bus
10 samples
Post-fader send to bus
8 samples
Pre-fader send to bus
8 samples
Post-fader send to bus
12 samples
Hardware sends also produce delays (see below).
Using Hardware I/O
When an audio interface is used on an insert or send, there is delay introduced by going through the D/A and A/D converter pair (for analog devices) or digital I/O connection (for digital devices) on the audio interface.
You can define a delay value for hardware inserts in the I/O Setup dialog. See the Pro Tools
Reference Guide for more information.
The following tables list the delay incurred by each type of analog and digital output available in Pro Tools|HD systems.
Pro Tools|HD I/O characteristics
Interface and
I/O Port
Stereo Mixer
192 I/O or
192 Digital
I/O
AES/EBU
24 samples
103 samples 192 I/O
Analog
96 I/O
AES/EBU
96 I/O
Analog
21 samples
79 samples
Surround
Mixer
22 samples
103 samples
19 samples
77 samples
I/O characteristics for Pro Tools|24 MIX-series Legacy interfaces connected to Pro Tools|HD Legacy Port
Interface and
I/O Port
Stereo Mixer Surround
Mixer
18 samples 16 samples 888|24 I/O
AES/EBU
888|24 I/O
Analog
82 samples 80 samples
20 samples 18 samples 888|20 I/O
AES/EBU
888|20 I/O
Analog
ADAT Bridge
Optical
ADAT Bridge
S/PDIF
18 samples
18 samples
76 samples
16 samples
16 samples
74 samples
1622 I/O
Optical
1622 I/O
S/PDIF
18
76
16 samples
74 samples
On the 888|24 I/O, the Digital I/O delay incurred when using AES/EBU or S/PDIF is identical.
120 Pro Tools|HD Getting Started Guide
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Table of contents
- 3 Contents
- 7 Welcome to Pro Tools|HD
- 7 Pro Tools|HD Systems
- 7 Pro Tools|HD (for PCIe) Systems
- 7 Pro Tools|HD (for PCI) Systems
- 8 Included with Pro Tools|HD Systems
- 8 Pro Tools HD Capabilities
- 8 Audio Recording and Playback Capabilities
- 9 Pro Tools Hardware Overview
- 9 Pro Tools|HD (for PCIe) Hardware
- 9 Accel Core (for PCIe) Card
- 9 HD Accel (for PCIe) Card
- 10 Pro Tools|HD (for PCI) Hardware
- 10 HD Core (for PCI) Card
- 10 HD Accel (for PCI) Card
- 11 TDM FlexCable
- 11 Audio Interfaces
- 11 192 I/O Audio Interface
- 12 192 Digital I/O Audio Interface
- 12 96 I/O Audio Interface
- 12 96i I/O Audio Interface
- 13 Optional Legacy I/O Audio Interfaces
- 13 System Requirements
- 13 MIDI Requirements
- 14 Hard Drive Requirements
- 14 Avoid Recording to the System Drive
- 14 Drive Formats
- 14 SCSI Hard Drives
- 14 FireWire Hard Drives
- 14 IDE/ATA/SATA Hard Drives
- 15 Hard Disk Storage Space
- 16 Digidesign Registration
- 16 About the Pro Tools Guides
- 16 Conventions Used in This Guide
- 17 About www.digidesign.com
- 19 Windows Installation
- 19 Installation Overview
- 19 Configuring Your Computer
- 19 Configuring the System BIOS
- 20 Configuring the SCSI BIOS
- 20 Modifying the Computer’s SCSI BIOS
- 20 Updating the ATTO SCSI BIOS
- 21 Installing SCSI Drivers
- 21 Installing the ATTO SCSI Driver
- 21 Windows System Optimization
- 21 Required Optimizations
- 22 Enabling DMA
- 22 Disabling System Standby and Power Management
- 22 Disabling ClearType Font Smoothing
- 23 Recommended Optimizations
- 23 Optional Optimizations
- 23 Disabling Network Cards
- 23 Adjusting Processor Scheduling
- 24 Disabling Hyper-Threading
- 24 Disabling System Startup Items
- 25 Hard Drive Configuration and Maintenance
- 25 Avoid Recording to the System Drive
- 25 Formatting an Audio Drive
- 25 Defragmenting an Audio Drive
- 26 Installing Pro Tools Hardware
- 26 Disabling Driver Signing Warnings
- 26 Installing Pro Tools|HD Cards
- 27 Connecting Pro Tools|HD Cards
- 28 Connecting Audio Interfaces
- 29 Connecting Loop Sync
- 29 Connecting Legacy Audio Interfaces
- 31 Connecting an Additional 16 Channels of Audio with Legacy Audio Interfaces
- 32 Installing Pro Tools HD Software
- 32 Installing QuickTime
- 33 Optional Software on the Pro Tools Installer CD
- 33 Digidesign ASIO Driver
- 33 Digidesign WaveDriver
- 33 Digidesign Ethernet Software for Control Surface Support
- 34 Pro Tools Demo Session
- 34 MacDrive Demo
- 34 Removing Pro Tools
- 35 Macintosh Installation
- 35 Installation Overview
- 35 Macintosh System Optimization
- 35 Turning Off Software Update
- 36 Turning Off Energy Saver
- 36 Setting Processor Performance
- 36 Disabling Spotlight Indexing
- 36 Disabling the Spotlight Shortcuts
- 36 Disabling Dashboard and Exposé
- 36 Enabling Journaling for Audio Drives
- 37 Hard Drive Configuration and Maintenance
- 37 Avoid Recording to the System Drive
- 37 Formatting an Audio Drive
- 37 Installing Pro Tools Hardware
- 37 Installing Pro Tools|HD Cards
- 40 Connecting Pro Tools|HD Cards
- 43 Connecting Audio Interfaces
- 44 Connecting Loop Sync
- 44 Connecting Legacy Audio Interfaces
- 46 Connecting an Additional 16 Channels of Audio with Legacy Audio Interfaces
- 47 Installing Pro Tools HD Software
- 48 Digidesign CoreAudio Driver
- 48 Optional Software on the Pro Tools Installer CD
- 48 Standalone CoreAudio Driver
- 48 Pro Tools Demo Session
- 48 Removing Pro Tools
- 49 Launching and Configuring Pro Tools
- 49 Checking the System
- 49 Starting Up Your System
- 49 Running DigiTest
- 51 Errors and Undetected Cards
- 51 Identifying Digidesign Cards with DigiTest
- 51 Viewing Card Information with DigiTest
- 52 Updating Audio Peripheral Firmware with DigiTest
- 52 Launching Pro Tools
- 52 Configuring Pro Tools
- 52 Pro Tools System Settings
- 53 Hardware Buffer Size
- 53 RTAS Processors
- 54 CPU Usage Limit
- 54 Number of Voices
- 55 Default Sample Rate
- 55 Delay Compensation Engine
- 56 DAE Playback Buffer Size
- 57 System Memory Allocation
- 57 MIDI Studio Setup
- 57 Audio MIDI Setup (AMS)
- 57 Pro Tools Hardware Settings
- 57 Default Sample Rate
- 58 Clock Source
- 58 Configuring Audio Interfaces
- 63 Configuring I/O Setup
- 64 Routing a Pro Tools Output Pair to Multiple Destinations
- 64 Backing Up your System Configuration
- 65 Connecting Your Studio
- 65 Setting Up Your Studio
- 66 Example Studio Setup with a Mixing Console
- 67 Example Studio Setup without a Mixing Console
- 68 192 I/O
- 68 192 Digital I/O
- 68 96 I/O
- 68 96i I/O
- 68 Connecting Equipment with Digital Audio Ins and Outs
- 69 Connecting Effects Units
- 69 Connecting Effects Units Digitally
- 70 Connecting MIDI Devices
- 70 Connecting SMPTE Synchronization Devices
- 70 Digidesign SYNC I/O
- 71 Connecting Ethernet Control Surfaces
- 71 Windows
- 71 Macintosh
- 73 Working with Pro Tools
- 73 Session Basics
- 73 Starting a Session
- 74 Main Windows
- 76 Rulers
- 76 Timebase Rulers
- 76 Conductor Rulers
- 76 Setting a Tempo
- 77 Using the Click Plug-In
- 77 Click Parameters
- 78 Using an External MIDI Click
- 78 Saving Sessions
- 79 System Resources and Settings
- 79 Playback Engine Dialog
- 79 System Usage Window
- 80 Transport Controls
- 81 Tracks
- 82 Audio Tracks
- 83 MIDI Tracks
- 83 Instrument Tracks
- 84 Region List
- 84 Navigating in a Session
- 85 Memory Locations
- 86 Viewing and Zooming
- 87 Zoom Toggle
- 87 Zoom Presets
- 87 Using Memory Locations for Zoom Control
- 88 Importing Data into Pro Tools Sessions
- 88 Importing Audio
- 88 Importing MIDI
- 89 Importing Files from Windows Explorer and Macintosh Finder
- 89 Basic Recording
- 89 Preparing for Recording
- 90 Setting Input Levels
- 90 Setting Reference Levels
- 90 Recording an Audio Track
- 91 Recording To and From Digital Devices
- 91 Setting Digital Format and Clock Source
- 92 Recording to and from an ADAT
- 93 Recording MIDI
- 96 Editing
- 96 Edit Modes
- 96 Edit Tools
- 97 Playlists and Nondestructive Editing
- 97 Editing Regions
- 99 Mixing
- 100 Basic Signal Routing
- 100 Send and Return Submixing for Effects Processing
- 101 Master Faders
- 102 Plug-Ins
- 103 Mix Automation
- 103 Final Mixdown
- 104 Using Dither on Mixdown
- 104 Sample Rate Conversion on Mixdown
- 105 Connecting SCSI Drives
- 105 SCSI Requirements
- 106 SCSI Cables
- 106 Distribute Audio Across Multiple Drives
- 106 Separate Video and Audio Files
- 106 Dual-Channel SCSI HBA Cards
- 106 Connecting SCSI Drives
- 107 SCSI Termination
- 107 Quick Formatting SCSI Drives
- 108 Initializing a Macintosh Drive
- 108 Initializing a Windows Drive
- 108 General Hard Drive Maintenance
- 108 Formatting Drives
- 109 Partitioning Drives
- 109 Seek Times on Partitioned Drives
- 109 Avoiding File Fragmentation
- 110 Optimizing (Defragmenting) Drives
- 110 Backing Up Data Before Optimizing
- 110 Using Macintosh Drives on Windows Systems
- 110 Formatting and Maintaining HFS+ Drives
- 111 DigiTest Error Codes
- 113 Configuring MIDI Studio Setup (Windows Only)
- 113 MIDI Studio Setup
- 113 MIDI Studio Setup Window
- 113 Interface Controls
- 114 Instrument List
- 114 Properties Section
- 115 MIDI Patch Name Support
- 117 Configuring AMS (Mac OS X Only)
- 117 Audio MIDI Setup
- 120 MIDI Patch Name Support
- 121 DSP-Induced Delays in Mixing
- 121 Introduction to DSP-Induced Delay
- 122 When to Compensate
- 122 How to Compensate
- 122 Automatically Compensating for Delays
- 122 Delay Compensation
- 123 TimeAdjuster and Delay Compensation
- 123 Manually Compensating for Delays
- 124 Using TimeAdjuster TDM Plug-In
- 125 Nudging Audio Tracks
- 125 Sample Rate and How it Affects Delay
- 125 Delay Factors
- 125 Bouncing Tracks
- 125 Using Plug-In Inserts
- 126 Using Sends
- 126 Using Hardware I/O
- 127 TDM Mixing and DSP Usage
- 127 Benefits of TDM II
- 127 TDM (or TDM I)
- 128 TDM II
- 129 DSP Allocation
- 129 DSP Allocation Basics
- 129 Mixing and DSP Usage
- 129 DSP Manager
- 130 Monitoring DSP Usage
- 131 Setting up Sessions to Use DSP Efficiently
- 131 DSP Usage and Mixer Plug-Ins
- 131 Understanding Mixers
- 132 Submixing
- 132 Mixers and DSP Hardware
- 134 48-Bit Mixing Precision
- 134 Mixer Headroom
- 134 Mixer Automatiion
- 135 Stereo and Surround Dithered Mixers
- 135 A Note About Dithering to 16-Bit and Dither Plug-Ins
- 135 Mixer Plug-Ins
- 136 Plug-In Features
- 136 Standard Surround and Stereo Mixers
- 136 Surround Dithered and Stereo Dithered Mixers
- 136 Switching Mixer Plug-Ins
- 136 Mixer Usage Guidelines
- 137 DSP Usage with TDM PlugIns
- 139 Troubleshooting
- 139 Backing Up Your Work
- 139 Backing Up Your Session Data
- 139 Backing Up Your System Configuration
- 139 Common Issues
- 139 Pro Tools Won’t Launch
- 139 Problem
- 139 Possible Solutions
- 140 Audio Interface Is Not Recognized
- 140 Problem
- 140 Possible Solutions
- 140 Using DigiTest as a Diagnostic Tool
- 140 Performance Factors
- 141 Before You Call Digidesign Technical Support
- 141 Register Your System
- 141 Use Digidesign Resources
- 141 Gather Important Information
- 141 System Information
- 142 Diagnostic Information
- 143 Index