Texas Instruments PurePath TAS5766M User manual

TI Information – Selective Disclosure Application Report
SLOU – August 2015
1
PurePath™ Smart Amp User Manual (TAS5766M/68M)
Jorge Arbona High Performance Analog / Audio
ABSTRACT
PurePath™ Smart Amp provides powerful tools to make speaker characterization and tuning
easy.
Smart Amp replaces traditional continuous power design principles and hardware based
speaker protection methods with algorithms that allow significant increases in peak power
output, loudness and sound quality relative to conventional amplifiers.
Smart Amp tools allow developers to understand how speakers are performing in the
system and then make informed decisions to improve performance. The algorithms,
characterization and tuning tools allow developers to overcome a wide variety of audio
challenges.
WARNING: EXPORT NOTICE
Recipient agrees to not knowingly export or re-export, directly or indirectly, any product or
technical data (as defined by the U.S., EU, and other Export Administration Regulations)
including software, or any controlled product restricted by other applicable national
regulations, received from Disclosing party under this Agreement, or any direct product of such
technology, to any destination to which such export or re-export is restricted or prohibited by
U.S. or other applicable laws, without obtaining prior authorization from U.S. Department of
Commerce and other competent Government authorities to the extent required by those laws.
This provision shall survive termination or expiration of this Agreement.
According to our best knowledge of the state and end-use of this product or technology, and in
compliance with the export control regulations of dual-use goods in force in the origin and
exporting countries, this technology is classified as follows:
US ECCN: 3E991
EU ECCN: EAR99
And may require export or re-export license for shipping it in compliance with the applicable
regulations of certain countries.

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2PurePath™ Smart Amp User Manual (TAS5766M/68M)
Contents
1General Overview............................................................................................................................4
1.1 Supported Smart Amp Devices.................................................................................................4
1.2 Migrating from Previous Versions of Smart Amp.......................................................................4
1.3 What is Smart Amp?..................................................................................................................5
1.4 Smart Amp Features .................................................................................................................6
1.5 Smart Amp Development Overview ..........................................................................................7
1.6 What’s Needed..........................................................................................................................8
1.6.1 Obtaining TI Hardware and Software ............................................................................9
1.6.2 Miscellaneous Equipment............................................................................................10
1.7 Things to Consider During Development.................................................................................11
1.7.1 Leading up to Engineering Validation Test (EVT)........................................................11
1.7.2 Leading up to Design Validation Test (DVT) and Mass Production (MP)....................11
2Software Installation.....................................................................................................................12
2.1 PurePath™ Console 3 Installation...........................................................................................12
2.2 MATLAB Runtime Installation..................................................................................................12
2.3 Getting Smart Amp Apps.........................................................................................................13
3Loudspeaker Characterization.....................................................................................................14
3.1 Characterization Process ........................................................................................................14
3.2 Characterization Summary Page.............................................................................................15
3.3 Saving a Characterization .......................................................................................................15
4Smart Amp Tuning........................................................................................................................16
4.1 Tuning Preparation..................................................................................................................17
4.2 Smart Bass Tuning..................................................................................................................18
4.2.1 Bass Enhancement (Low Volume Tuning) ..................................................................19
4.2.2 Morphing Control (Mid- to High- Volume Tuning)........................................................
21
4.2.3 Harmonic Bass Alignment (Mid- to High- Volume Tuning)..........................................22
4.2.4 Excursion Tuning (Optional)........................................................................................22
4.3 Smart EQ.................................................................................................................................23
4.4 Digital Gain Control .................................................................................................................26
4.5 Snapshots ...............................................................................................................................26
4.6 Saving a Tuning ......................................................................................................................26
5Hardware Design...........................................................................................................................27
5.1 Power Supply Rail Voltage......................................................................................................28
5.2 Power Supply Current at Audio Frequencies ..........................................................................29
5.3 Power Supply Current at Higher Frequencies.........................................................................31
5.4 Post-processing Considerations..............................................................................................31
6Software Implementation and Verification..................................................................................33
6.1 Importing the Speaker Parameters into the Smart Amp Target EVM App..............................34
6.2 Calibrating the System Gain in the End-System .....................................................................35
6.3 Smart Amp Register Dump into a Header File........................................................................37
6.3.1 Working with Non-Standard Configurations.................................................................39
6.4 Integrating the Output Header File into the End-System.........................................................40
6.5 Smart Amp Verification in the End-System .............................................................................40
6.6 Changing Device Parameters On-the-fly in the End-System ..................................................42
7Support...........................................................................................................................................43
References.............................................................................................................................................44
Appendix A. Supported Speaker Configuration Types .....................................................................45
A.1 Free Field / Single Speaker in Box..........................................................................................46

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PurePath™ Smart Amp User Manual (TAS5766M/68M) 3
A.2 Left and Right Drivers in the Same Box..................................................................................47
A.3 Parallel/Series Drivers in the Same Box (no analog crossover)..............................................48
A.4 Parallel Drivers in the Same Box (analog crossover)..............................................................49
Appendix B. Smart Amp End-System Implementation Checklist.....................................................50
Appendix C. MATLAB Compiler Runtime Troubleshooting..............................................................51
Revision History....................................................................................................................................52
Trademarks............................................................................................................................................52
Figures
Figure 1. PurePath™ Smart Amp Block Diagram............................................................................5
Figure 2. Smart Amp Development Overview..................................................................................7
Figure 3. mySecureSoftware Page ...................................................................................................9
Figure 4. Verification of MATLAB Compiler Runtime Installation ...............................................12
Figure 5. Smart Amp Tuning Process ............................................................................................16
Figure 6. Smart Amp Tuning Page..................................................................................................18
Figure 7. Digital Gain Control..........................................................................................................26
Figure 8. Audio Clip A, 22dB Peak to Average Ratio Source.......................................................27
Figure 9. Audio Clip B, 9dB Peak to Average Ratio Source.........................................................27
Figure 10. Effects of Decoupling for Audio Frequencies ...............................................................29
Figure 11. Power Supply Current Measurement .............................................................................30
Figure 12. Smart Amp Signal Chain .................................................................................................31
Figure 13. End-System Integration...................................................................................................37
Figure 14. Dump to Header File Page...............................................................................................38
Figure 15. Example Header File Output Snippet .............................................................................39
Figure 16. Example Header File Output Snippet .............................................................................40
Figure 17. Volume Control Change Comparison ............................................................................42
Figure A-2. Obtaining the Loudspeaker Diameter ............................................................................
45
Figure A-3. Speaker Element Types...................................................................................................45
Figure C-1. Editing Windows System Variables................................................................................51
Tables
Table 1. Equipment and Software ...................................................................................................8
Table 2. Miscellaneous Equipment ...............................................................................................10
Table 3. Microphones Tested for Smart SPL and Passive Radiator Systems ..........................10
Table 4. Bass Enhancement Parameters......................................................................................19
Table 5. Example Smart Amp Supply Rail Voltages for the TAS5766M.....................................28
Table 6. Peak Input Current Examples (One Channel)................................................................30
Table 7. TAS5766M/68M Post-processing Gain Controls ...........................................................32
Revision History....................................................................................................................................52

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4PurePath™ Smart Amp User Manual (TAS5766M/68M)
1 General Overview
Chapter 1describes Smart Amp, its features and the hardware and software tools required for
evaluation and development.
Chapter 2describes how to install the PurePath™ Console 3 software.
Chapter 3discusses how to perform a speaker characterization.
Chapter 4explains how to tune loudspeakers with Smart Amp.
Chapter 5helps the design engineer understand how to assess current requirements, and then
determine the supply voltage levels and the current needed for Smart Amp. With that knowledge
the designer can adapt conventional power systems to peak output power needs of Smart Amp
designs.
Chapter 6explains how to transfer the Smart Amp code into a microcontroller so that coefficients
can be downloaded into Smart Amp in the end-system at start-up.
For support, please refer to Chapter 7.
For a list of supported speaker configurations, refer to Appendix A.
1.1 Supported Smart Amp Devices
This document supports the following Smart Amp devices:
1. TAS5766M
2. TAS5768M
1.2 Migrating from Previous Versions of Smart Amp
PurePath™ Console 3 can import snapshot (.cnsss3) files from PurePath™ Console 1.
Snapshot files can be created from .ccdef files, if necessary. Refer to the PurePath™ Console 1
Quick Start User’s Guide for details on how to create snapshots.

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1.3 What is Smart Amp?
Conventional hardware-based speaker protection matches the continuous power output of the
audio amplifier with the speaker output rating and sometimes incorporates high pass filtering to
prevent over-excursion. PurePath™ Smart Amp replaces hardware based speaker protection
methods with predictive algorithms, speaker characterization tools and real-time signal
monitoring to increase the peak output of the speaker without damage.
The first implementation step of Smart Amp based audio solutions is characterizing the speaker
with TI’s PurePath™ Console 3 and the PurePath™ Learning Board. These are powerful, easy-
to-use tools designed specifically to simplify system level characterization, tuning and
implementation. The characterization process creates a digital model of the speaker based on
thermal, electro-mechanical and acoustic parameters.
The output of the characterization process is an initial set of coefficients that define the Safe
Operating Area (SOA) which establishes the boundaries of maximum speaker diaphragm
excursion and voice-coil temperature during operation. If the SOA is set correctly, the audio
engineer need not worry about speaker damage during the audio tuning process – depending on
how hard the system is pushed audio might sound more or less desirable, but speaker safety is
ensured if configured properly.
EQ / Volume Smart Bass Protection Amp
Smart Amp Control Algorithm
Automatic
bass response
alignment
Smart SOA Smart Sense*
PurePath™
Smart Amp
Thermal,
Excursion
*Feedback systems
I/V, Supply,
Temperature
Helps keep
loudspeaker
within SOA
Audio
Input
Closed-loop
Class-D Amp
Smart EQ
Automatically
tunes high
frequencies
Figure 1. PurePath™ Smart Amp Block Diagram
PurePath™ Smart Amp technology enables significant sound quality and system reliability
improvements while reducing component size and cost. The PurePath™ Console 3 graphical
user interface and Learning Board speaker characterization hardware provide simple
configuration of advanced properties fully describing an audio system’s acoustical, electrical,
thermal and reliability capabilities and simplifying system level characterization, tuning and
integration.

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6PurePath™ Smart Amp User Manual (TAS5766M/68M)
Automatic
Bass Compensation Morphing
Smart SPL
Smart EQ Smart EQ
Smart SOA
1.4 Smart Amp Features
Smart Bass
Bass can easily be extended into any alignment
automatically. As signal amplitude is increased in
the bass region, Smart Bass automatically
morphs the response to accommodate for larger
excursion.
Smart SPL
High-frequency behavior of the loudspeaker diaphragm
cannot be obtained electrically. Similarly, it is difficult to
obtain accurate low-frequency acoustical measurements
without an expensive anechoic chamber. Smart SPL
automatically merges electrical and acoustical measurements
to create a full picture of the SPL response.
Smart EQ
Automatically tunes high frequencies to
deliver a flat response or match a target
curve in seconds. And it does it very
efficiently, too.
Thermal and Excursion Protection
The Smart Amp algorithm understands the thermal and
excursion limitations of the speaker. This allows to drive it
at peak levels much louder than conventional amplifiers
while keeping the voice coil temperature and excursion
within the specified limits. This results in louder audio
playback.

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1.5 Smart Amp Development Overview
The following steps summarize Smart Amp evaluation, planning, characterization, tuning and
integration:
Obtain Hardware and
Software
Plan for Development
Obtain Speaker
Parameters
Tune Speaker
End-system Integration
Complete!
Figure 2. Smart Amp Development Overview
1. Obtain Hardware and Software – Speaker characterization and tuning are performed
using the PurePath™ Console 3 software. The TI Learning Board and the Smart Amp
Target EVM are needed in order to fully evaluate and develop with Smart Amp. Refer to
Section 1.6 for details.
2. Plan for Development – Developing Smart Amp based systems for the first time can be
different than working with conventional amplifiers. Information obtained during the
speaker characterization process often leads to changes to the speaker or enclosure to
maximize output and quality. See Section 1.7 for tips on development.
3. Obtain Speaker Parameters – The next step is to understand the characteristics of the
speaker to be tested. This is covered in Chapter 3. Once a speaker is characterized, the
ppc3 file obtained from this step will be used on the next step.
4. Tune Speaker – Once the speaker data is obtained, a speaker can be tuned using the
Learning Board or the Target EVM by importing a ppc3 file. Refer to Chapter 4.
5. End-system Integration – Smart Amp fundamentally shifts how audio systems are
designed. Using the Smart Amp tool set, a designer gathers an in-depth understanding of
speaker electro-mechanical, thermal and acoustic parameters. Based on these
parameters, Smart Amp algorithms deliver high peak voltage and current to the speaker
while protecting the speaker from excessive heat or movement. Increased voltage and
current levels lead to changes in the system power design. For these reasons it is
important to understand the power supply requirements early in the design. This is
covered in Chapter 5. Software implementation is discussed in Chapter 6.

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8PurePath™ Smart Amp User Manual (TAS5766M/68M)
1.6 What’s Needed
The table below shows the hardware and software requirements organized by configuration type
(e.g. 2.0, 2.1 or 4 channel). All the configurations require the Learning Board for
characterization. The Target EVM is required to generate code to be implemented in the end-
system.
Table 1. Equipment and Software
2 Channel Mid-Power
Smart Amp
2.1 Channel Mid-Power
Smart Amp
4 Channel Mid-Power
Smart Amp
Hardware Tools (1.6.1)
PurePath™ Smart Amp Learning Board x x x
PurePath™ Console Motherboard x x x
Target EVM (1.6.1)
2 Channel TAS5766M EVM (TSSOP) x
4 Channel TAS5766M EVM (QFN) x x
Miscellaneous Equipment (1.6.2)
Weigh Scale o o o
Adhesive Putty o o o
Metric Ruler o o o
24V Power Supply x x x
Microphone p p p
Software Tools (1.6.1)
PurePath™ Console 3 x x x
x= required, o= optional, p= required for Passive Radiator / Smart SPL

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1.6.1 Obtaining TI Hardware and Software
TI approval is required to order Smart Amp-related hardware and software. Click the
button in the Target EVM web site to begin the approval process. Once approved, the user will
receive an email confirming access to the mySecureSoftware web site and hardware ordering
information.
The PurePath™ Console 3 software can be downloaded from the PUREPATHCONSOLE
Software Product page in mySecureSoftware, as shown below. There is no need to download
separate plugins – Smart Amp Apps will automatically be available within PurePath™ Console 3
once the user is given access to the proper Software Product (e.g. TAS5766MSW-SA, etc.).
The Target Software Product, as shown in Figure 3, contains hardware ordering information,
documentation, videos, etc.
Figure 3. mySecureSoftware Page
Please contact [email protected] for any issues related to software access.
Target Software Product: Hardware ordering information, documentation,
videos, etc.
PurePath Console 3 Software

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1.6.2 Miscellaneous Equipment
In order to perform a full characterization the following hardware is recommended. Some of
these items are not needed if loudspeaker parameters are known.
Table 2. Miscellaneous Equipment
Equipment Description
Weight Scale 20g in 1mg increments preferred. The Gemini-20 Portable Milligram Scale
by American Weigh is recommended. Not required if the force factor Bl is
provided by the speaker manufacturer.
Adhesive Putty Similar to Blu Tack or Removable Adhesive Putty by Scotch. Not required
if the force factor Bl is provided by the speaker manufacturer.
Metric Ruler Size depends on loudspeaker diaphragm area (Sd). Also used to
measure port area (Sp). Plastic is preferred to prevent the magnet from
pulling the ruler. Not required if Sdand Spparameters are known.
24V Power Supply A lab power supply capable of providing peak power to the speakers. A
24V, 6A supply addresses most circumstances. An external AC/DC
supply could be used as well, such as the MENB1100A2403F01 by SL
Power Electronics.
A microphone is required for Smart SPL and characterizing passive radiator systems. Below is a
list of microphones that have been tested for Smart Amp.
Table 3. Microphones Tested for Smart SPL and Passive Radiator Systems
Model Manufacturer Type
Mic: CME-1538-100LB CUI, Inc. Electret Condenser
(requires external 1.8V bias)
Capsule: 4938
Preamp: Type 2670 Brüel & Kjær ¼” Diameter Pressure Field
Mic: EMM-6
Dayton Audio ½” Diameter Condenser (tested with Shure X2u USB Preamp)
Mic: iMM-6 Dayton Audio Condenser
(requires external 1.8V bias)

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PurePath™ Smart Amp User Manual (TAS5766M/68M) 11
1.7 Things to Consider During Development
Characterization and tuning speakers provide previously unavailable information on the
loudspeaker performance and how to improve it. Most customers find this leads to changes in
the system. These changes to improve performance can affect the timeline if this isn’t taken into
account up front.
1.7.1 Leading up to Engineering Validation Test (EVT)
Do
•Create an acoustic mock-up of the audio system and use the Learning Board to start
characterization and tuning.
•Request working/non-working prototypes of systems for use as acoustic test platforms.
•Start characterization as early as possible.
•Audition speakers in the acoustic mock up.
•Work out how the Smart Amp code will be downloaded during start up and how much
time is needed to boot Smart Amp.
•Set clear performance targets.
•Use characterization and tuning results to work with speaker vendor to improve the
sound or performance of transducers.
Do not
•Wait for first board build to start speaker characterization and tuning prior to EVT.
1.7.2 Leading up to Design Validation Test (DVT) and Mass Production (MP)
Do
•Start characterization and tuning of EVT systems as early as possible.
•Use EVT characterization and tuning results to work with speaker vendor to improve the
sound or performance of transducers.
•Modify the EVT and DVT prototypes with external switches and wires so that the Smart
Amp EVM can be connected to it.
•Set internal reviews of the tuning.
•To speed up response time, aim to provide common working prototypes to TI and
speaker vendors, if necessary.
•Work to ‘freeze’ the acoustic elements by DVT. Acoustic freezes allow adequate time for
fine tuning the sound for MP.

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12 PurePath™ Smart Amp User Manual (TAS5766M/68M)
2 Software Installation
The following software is required to run Smart Amp.
1. PurePath™ Console 3
2. MATLAB Runtime
Smart Amp-related Apps are downloaded directly from PurePath™ Console 3 using its App
Center (refer to Section 2.3).
2.1 PurePath™ Console 3 Installation
Refer to the PurePath™ Console 3 documentation for installation details.
2.2 MATLAB Runtime Installation
The Smart Amp software requires the MATLAB Compiler Runtime (MCR) 7.16 engine in addition
to the PurePath™ Console 3 installation to run. The installer for MCR should automatically
install when installing PurePath Console 3. After installation, you may check the list of installed
programs (On Windows 7, this is accessible via Control Panel > “Programs and Features”) to
verify that “MATLAB Compiler Runtime” is installed.
Refer to Appendix C for related troubleshooting information.
Figure 4. Verification of MATLAB Compiler Runtime Installation

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PurePath™ Smart Amp User Manual (TAS5766M/68M) 13
2.3 Getting Smart Amp Apps
PurePath™ Console 3 Apps are downloaded using the App Center .
Follow these steps to download Smart Amp specific Apps:
1. Download the PurePath™ Console 3 software from the PUREPATHCONSOLE Software
Product in mySecureSoftware. Refer to the PurePath™ Console 3 documentation for
installation details.
2. Once PurePath™
Console 3 is installed,
click the Sign in
button as shown to
the right.
3. Smart Amp-related
Apps will now appear
in the Available EVM
Apps section. If no
Smart Amp Apps
appear refer to
Section 1.6.1.
4. Click the desired
App(s) to open the
information window
and click Install.
5. The App(s) will now appear in the Installed EVM Apps section.

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14 PurePath™ Smart Amp User Manual (TAS5766M/68M)
3 Loudspeaker Characterization
The main objective of the loudspeaker characterization is to obtain the electro-mechanical and
thermal parameters and establish the safe operating area (SOA) of the loudspeaker system. The
electro-mechanical and thermal parameters are obtained using the Learning Board.
The Learning Board App has a step-by-step wizard that guides the user through the entire
loudspeaker characterization process.
3.1 Characterization Process
To perform a loudspeaker characterization:
1. Connect the Learning Board to your PC using the USB cable.
a. Provide a power supply.
b. Do not connect the speakers yet.
2. In PurePath™ Console 3, open the
Learning Board App and select New.
3. If the Learning Board is shown as offline,
click Connect.
4. Click Characterization.
5. Follow the step-by-step
wizard until the
characterization is
complete.
6. Once complete, the Characterization Summary page will be shown.

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3.2 Characterization Summary Page
The Characterization Summary page shows the results of the loudspeaker characterization.
To verify the loudspeaker plots, use the controls to the top of the graph:
Driver and enclosure parameters are also shown as well as the established safe operating area
(SOA).
If desired, click the button to redo the characterization. The button will bring back the
Characterization Summary page.
3.3 Saving a Characterization
The characterization data can be saved by clicking the
button at the Title Bar and selecting Save. This will output a
.ppc3 file.
This .ppc3 file can later be imported into the Target EVM
App for tuning, as explained in Section 4.1.
Selects between Modeled SPL and Excursion or
Measured Impedance, Temperature and SPL plots.

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16 PurePath™ Smart Amp User Manual (TAS5766M/68M)
4 Smart Amp Tuning
Tuning is a process involving both subjective and methodical approaches. This section provides
guidelines to help establish a baseline to achieve the best possible tuning. The main objectives
of the (iterative) audio tuning process, also referred to as ‘voicing’, are:
•Improve bass performance using Smart Bass controls (Section 0) by adjusting:
- Bass Enhancement (Section 4.2.1)
- Morphing Control (Section 4.2.2)
- Harmonic Bass Alignment (Section 4.2.3)
•Improve high frequency response using Smart EQ (Section 4.3).
The Smart Amp Tuning Process is summarized in Figure 5.
Figure 5. Smart Amp Tuning Process
Good?
Tune
BASS ENHANCEMENT
Tune MORPHING control
Tune HARMONIC BASS
Tune Smart EQ
Play Music
Done!
no
yes
tune more
Section 4.2.1
Section 4.2.2
Section 4.2.3
Section 4.3

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4.1 Tuning Preparation
Tuning is performed using the Learning Board or the Target EVM.
1. Connect the Learning Board or Target EVM to your PC using the USB cable.
a. Provide a power supply (matching the one to be used in the final system).
b. Connect the loudspeaker.
2. In PurePath™ Console 3,
open the App that
corresponds to the board that
was connected (Learning
Board or Target EVM).
3. If the board is shown as
offline, click Connect.
4. Click Tuning and Audio
Processing.
5. Import the characterization data that was obtained during the Characterization process
(Chapter 3) by clicking the button.
6. Click and perform a System
Calibration. This process
ensures that the Smart Amp
algorithm is properly scaled
based on the amplifier output
gain.

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18 PurePath™ Smart Amp User Manual (TAS5766M/68M)
4.2 Smart Bass Tuning
During the characterization process, the low-frequency SPL model of the loudspeaker was
obtained. Based on this model, the response is automatically optimized to match popular
loudspeaker alignment types (e.g. Butterworth, Linkwitz-Riley, etc.). This allows the audio
engineer to focus on choosing the desired sound with just a few clicks.
When tuning Smart Bass for the first time, it is best to first disable the Equalizer (in the
page):
To start tuning Smart Bass, enable Smart Amp and
click the Expand symbol , as shown to the right.
The Smart Amp Tuning page has all the controls needed for Smart Bass tuning. Several plots
(such as Excursion) are provided as an aid to the tuning process.
Figure 6. Smart Amp Tuning Page
Section 4.2.2
Section 4.2.3
Section 4.2.1
Section 4.2.1
Section 4.2.4
Morphing
Harmonic Bass
Alignment

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4.2.1 Bass Enhancement (Low Volume Tuning)
The main objective is to maximize the bass response as much as
possible and tune the bass as desired. During this phase it is
important to listen at low volume levels only – this is to ensure that
thermal and mechanical protection systems do not kick-in. Ensure
that the Morphing Control (Section 4.2.2) is set at max during this
phase.
Table 4. Bass Enhancement Parameters
Field
Description
Corner Frequency -3dB point of the target response. Smaller speaker
drivers should use higher corner frequency.
Order (Slope) Determines the sharpness of the roll-off towards
lower frequencies. For lower corner frequency,
choose higher order.
Type Selects the alignment type.
Bass EQ To further enhance bass, as needed, at low volume
settings
Corner Frequency
The Corner Frequency indicates the -3dB point of a flat
response target (indicated by the green curve). Selecting a
proper Corner Frequency is important for the overall
performance of the speaker system. If the cutoff is set too
high, the speaker will have limited bass response. If set too
low, energy will be wasted trying to drive frequencies that the
speaker won’t be able to reproduce and the excursion
protection system will be overly active.
A ‘getting started’ setting is described in this section. It is
recommended to do a series of listening tests while adjusting
settings.
•Adjust Corner Frequency while watching the
compensation (red curve) in the response plot window.
•Targeting between a 10dB to 20dB compensation (red
curve) often provides the best results.
•Do not exceed the 20dB line (at least initially).
•In some situations it can be advantageous to leave
some gain headroom in favor of a general Bass EQ
(later step).
Good?
Set CORNER
FREQUENCY
Set alignment ORDER
(slope)
Set alignment TYPE
Tune BASS EQ
LISTENING TEST
at low volume levels
(e.g. -30dB)
yes
no
To Section 4.2.2

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20 PurePath™ Smart Amp User Manual (TAS5766M/68M)
Alignment Order and Type
The Order and Type determine the bass roll-off. In
other words, it determines what occurs below the
corner frequency.
A high-order roll-off cuts bass faster saving power and limiting speaker excursion that won’t
produce much SPL. Likewise, Type has significant influence on the SPL and energy below the
corner frequency.
•Select a higher order if the speaker handles excursion poorly.
•Select a lower order to leave small amounts of low-frequency content in the signal.
•Butterworth is suitable for most applications. For ported / passive radiator systems that
can reproduce 60-80Hz, a Chebyshev alignment works well.
Bass EQ (Optional)
It may be desired, for an even richer bass experience,
to extend the target curve (green line) using a
standard Bass EQ that can be shaped in amplitude,
frequency and Q. Bass EQ works well in concert with
the Morphing feature that dynamically cuts Bass as
excursion and thermal headroom drops with increase
in loudness. It is recommended to tune the EQ setting
at low volume initially. In subsequent steps (e.g.,
Morphing adjustment) the Bass EQ setting may be
revisited, especially if an aggressive boost has been
selected initially.
1. Set the Bass EQ to On.
2. Select Bandpass.
3. Select a Bass EQ Frequency within 1x to 2x that of the Corner Frequency setting.
4. Adjust Gain up, but keep the compensation (red curve) below 20dB (at least initially).
5. Tweak the Qvalue. Often, values between 0.5 and 3 work well.
Mono Bass Frequency
When enabled, Mono Bass Frequency is the cross over point below which the left and right
channels are mixed, effectively creating a mono signal below that frequency on both channels.
In systems with a common cabinet for left and right drivers this control ensures against the
possibility of a drop in the bass level due to phase mismatch between the left and right channel
signals.