MaxxBass Development Recommendations 1 Purpose The document provides recommendations on MaxxBass in evaluation, selection of possible implementations, circuit design and testing. It also refers to several other documents with additional details in specific areas. This document and other related materials can be found at www.maxx.com. 2 MaxxBass Benefits MaxxBass is a patented signal processing technology from Waves. It extends the perceived bass frequency response of almost any loudspeaker system by 1 to 1.5 octaves using a pyschoacoustic effect based on the Phenomenon of the Missing Fundamental. Since the most significant audio quality limitation in most audio systems is the loudspeaker bass response, MaxxBass offers the manufacturer a new tool to optimize acoustic system performance. The designer can choose to use MaxxBass to improve the bass response 1-1.5 octaves, lower speaker enclosure volume, lower power consumption or some combination of these to best meet their market requirements. Some current applications include Improve bass response of existing subwoofer systems Reduce volume or power requirements of subwoofers and still keep the same relative acoustic performance Reduce power consumption and improve battery life in portable systems Compensate for a med-bass frequency gap where small satellites speakers in home theater systems do reproduce frequency down to the subwoofer crossover. Improve the bass response in space limited LCD TVs and notebook PCs. 3 Evaluation Products and Procedures Waves offer customers both hardware and software evaluation tools for MaxxBass described here. May 2004 1 www.maxx.com
3.1 MaxxBass 102 The MaxxBass 102 is a good initial evaluation system for MaxxBass. It supports simple stereo line-in and line-out on RCA connectors. It is simple to use for evaluation with most consumer electronic devices. More information including detailed documentation on how to use this system in evaluating MaxxBass can be found at www.maxx.com. The MaxxBass 102 is shown in Figure 1. The system has controls for input attenuation, MaxxBass Intensity, fully variable MaxxBass Frequency, and bypass. The variable MaxxBass Frequency control is convenient for testing and tuning to a wide range of acoustic designs. One limitation is that no output gain stage is included so the overall signal strength is reduced. Figure 1. MaxxBass 102 3.2 MX3000AS Reference Design Waves has a simple 2-layer PCB reference design for the MX3000AS. This is a low cost implementation suitable for consumer electronics. Complete gerber file layout and schematics are available at www.maxx.com. The MX3000AS Reference Design shown in Figure 2 has two fixed crystals at 5 and 8 Mhz, so the system can support only two MaxxBass Frequencies of roughly 50 and 80Hz. To set the system for other MaxxBass Frequencies, the crystals can be replaced. This system has input and output level controls, as well as controls for two MaxxBass Frequencies, MaxxBass Intensity, bypass, and fixed 100Hz LPF. May 2004 2 www.maxx.com
Figure 3. MX3000AS Reference Design 3.3 Renaissance Bass Plug-in Waves also offers plug-in software that operates in any of the popular digital audio editing environments for evaluation. The Renaissance Bass plug-in is the second generation MaxxBass plug-in and provides the same functionality as the MaxxBass ASIC and other consumer software implementations. The user interface for Renaissance Bass is shown in Figure 3. The software can be downloaded for a free two week trial from www.waves.com. Please contact Waves if OEMs need an extended time authorization for further evaluation. Figure 3. Renaissance Bass User Interface May 2004 3 www.maxx.com
4 Types of MaxxBass Implementations Waves offers several different implementations for MaxxBass, so that cost-effective solutions are available for almost any application. 4.1 MX3000AS MaxxBass ASIC A low cost mixed signal ASIC, MX3000AS, is suggested for traditional analog based systems. The MX3000AS is packaged in a tiny 16-pin SOIC. It includes both a full custom DSP, sigma-delta ADC, DAC and high quality analog circuit for a complete MaxxBass DSP system. This product is purchased from directly from Waves or its authorized distributors. Its pricing includes patent royalties for MaxxBass, so no other expense is involved. Full MX3000AS information including datasheet, reference design and other materials is available at www.maxx.com. This document emphasizes design and testing recommendations for using the MX3000AS. 4.2 DSP Software Licensing For DSP based systems in areas such as home theater or automotive in-dash CD/Receivers it may be possible to operate the MaxxBass algorithm on existing DSPs used for other functions. MaxxBass DSP licensing is available for high volume consumer and automotive applications of 100Ku/yr and more. Waves has certified the MaxxBass algorithm on DSPs from AKM, Analog Devices, Motorola and Texas Instruments. Other porting and certifications are pending, so check the website for the latest status. The MaxxBass code can be ported to almost any audio DSP architecture. On a Motorola DSP563xx architecture, a MaxxBass stereo implementation requires about 10.5 MIPS, 240 words program and 31 words data. The system design flow is similar to designs with the MX3000AS ASIC except that the developer will implement the MaxxBass functionality by DSP code. 4.3 PC Software Licensing For personal computers it is recommended to implement MaxxBass in software directly on the host CPU. Waves has licensed Sony, who uses Renassiance Bass/MaxxBass in their Sonic Stage Mastering Studio application on all desktop and notebook PCs. Waves has also developed a solution for MaxxBass using a driver level solution in SigmaTel s PC codec driver architecture. This approach can be attractive as the MaxxBass function is then independent of any specific application and can be applied to all programs requiring audio output including music players, movie players, and games. May 2004 4 www.maxx.com
5 General Development Flow for MaxxBass Choose the implement type best suited to your needs ASIC, DSP or PC host Define speaker configuration 2.0, 2.1, 4.1, 5.1 etc Define and measure the acoustic roll-off of speakers (f3) Set initial MaxxBass Frequency at 70% of f3 (for example 70Hz on a loudspeaker with 100Hz f3). Tune through listening tests for optimal response. Set initial MaxxBass Intensity at maximum. This can be tuned to lower intensity settings using I2C commands. 6 MX3000AS Design Recommendations Designers using the MX3000AS should begin their efforts by reviewing the MX3000AS Reference Design which is available at www.maxx.com. Here are several additional suggestions that can help ensure that the best results are obtained. 6.1 Input level to MX3000AS The MX3000AS has a maximum input level of 1V peak-to-peak. It is important not to provide a higher level input, as the input level can clip. The MX3000AS has a soft clipping feature, so it does not sound as noticeable as traditional analog clipping. The main effect is that the MaxxBass improvement will be sharply degraded. 6.2 Input level to amplifier The MaxxBass adds a specific type of harmonics. The maximum gain with a full scale input is +6dB, so the input to the amplifier should be designed to support this amount of headroom. MaxxBass also implements a HPF function at the MaxxBass Frequency, so this can protect speakers from the most damaging low frequency energy. If the amplifier has a high distortion it will degrade the MaxxBass sound quality. 6.3 Choosing clock source A crystal oscillator or ceramic resonator clock source can be used. The MX3000AS datasheet discusses how to best select the initial clock frequency, and the final frequency should be choosen through acoustic listening tests. 6.4 Reset Circuit If a RC circuit is used for reset, this circuit should be designed carefully. Please see the MX3000AS datasheet for details. 6.5 MaxxBass capacitor May 2004 5 www.maxx.com
A 15ns MaxxBass capacitor Crc should be used for all MaxxBass Frequency settings. Previous versions of the MX3000AS datasheet indicated that this capacitor should be chosen based MaxxBass Frequency, which is not recommended. 6.6 Bypass capacitors Bypass capacitors to ground are required on all inputs and outputs. 6.7 Input and output decoupling capacitors 22pF to 33pF capacitors are needed on the audio input and output pins in order to avoid output oscillations. 6.8 Number of PCB Layers It is generally recommended that a 2 layer PCB design be used such as the MX3000AS Reference Design. More than 2 layers is OK. One layer designs can be used, but the reset sensitivity is much higher in these designs, so a digital Reset sequence is necessary. 6.9 Layout Suggestions It is suggested that the designer reuse the MX3000AS Reference Design as closely as possible. Some additional suggestions are 6.9.1 Keep the clock leads as short as possible. 6.9.2 Use wide trace lines of at least 15-20mils for conduction paths. 6.9.3 Keep decoupling capacitors has close to the MX3000AS as possible. 7 MaxxBass Prototype Tuning Recommendations It is recommended that several functions be added to the initial development PCB in order to simplify optimal tuning of MaxxBass in the production circuit. 7.1 MaxxBass Bypass Switch A MaxxBass bypass switch is very useful during the development phase to enable the user to disable MaxxBass during testing and tuning. It is desirable to have a red LED indicator illuminate during Bypass. This can remain or be eliminated in the production circuit. 7.2 Two MaxxBass Crystals or Ceramic Resonators It is helpful to have the initial PCB support two different clock frequencies, so that these can be compared and evaluated in the application circuit. Normally only one clock frequency would be used in the final circuit. May 2004 6 www.maxx.com
7.3 Peak detector on MX3000AS input A peak detector with yellow LED indicator is desirable for tuning. The LED should be illuminated if the peak reaches 1Vptp. 7.4 LPF requirements If MaxxBass is implemented in a subwoofer for a 2.1 audio system. It is recommended that first a L+R channels be added, and then a low pass filter (LPF) is used on the summed mono channel. The LPF output should then be connected to both L and R inputs of the MX3000AS. May 2004 7 www.maxx.com