Audio Calibration

Anthem Room Correction (ARC) System - Part 1


Advantages of a PC-based System for System Design

As algorithms are improved, all that is required is a software update. Updates to room correction systems that compute coefficients inside the AVR are rare. In fact, a manufacturer might not be able to make an update at all, even if a problem is identified. The memory containing the instructions for the DSP often cannot be changed externally. Removing the memory chip at the factory is next to impossible since it is a surface mount device on a multilayer board.

The coefficients calculated by the PC are transferred to the AVR so the DSP can go about the work it was designed to do. The PC to AVR interface also transfers test tones produced by the speaker during calibration. Newer generations of AVRs (hardware retrofit of a current product being extremely unlikely and expensive) with more powerful DSPs, allow more complex filters to be synthesized. For example, the number of frequency bands can be increased with an IIR filter structure. While the change in the software for Step 2 could be extensive, the interface from the PC to the AVR, to properly load the extended vector of coefficients to the DSP, would be minor.

More of a concern to the designer than the consumer is the fact that the code from the PC can work in many different brands of DSPs. Often a designer will select a board from an independent vendor which contains a complete DSP system. The board contains the DSPs, associated RAM, electrically programmable ROM (EPROM), and clocking systems. In addition the board contains chips to reformat the signals emerging from the DSP to interface to the DACs. It has chips to decode S/PDIF and other digital data formats such as the digital audio output of an HDMI receiver chip. The board will also contain a control port with a messaging system that may include the ability to reconfigure EPROM data which is required if the filter coefficients are to be loaded from the PC. Different products may use different vendors' boards and vendors may be changed for a new design. If a company does not have the resources to design its own PC based room correction system, it must fall back to whatever simple system the vendor offers as a firmware option.

While information on these types of modules is almost never presented in a public website, examples from Momentum Data System can be found at

Anthem does not use these predesigned boards in its Pre/Pros, but instead the Anthem boards are designed in-house. The MRX units use 3rd party DSP boards but not from Momentum Data Systems.

The take away here is that the important intellectual property of the ARC system is the program on the PC. Bug fixes and improvements in the ARC are completely independent of the hardware. This decoupling from hardware allows the Anthem room correction developers to produce one PC program for all products freeing up valuable resources that would be devoted to designing different code for different models.