User manual ALTEC LANSING 4048A SIGNAL PROCESSING

[. . . ] 4048A digital signal processor & Professional Altec Lansing Professional 1000 W. Suite 362 Oklahoma City, OK 73116 USA A division of Altec Lansing Technologies Inc, Milford PA 18337-0277 Made In USA Operating Manual -4048A digital signal processor Table Of Contents 1 2 3 4 5 6 7 8 9 INTRODUCTION . 5 PA AT R E A R PA N E L F E AT U R E S . 8 A LTEC LANSING MAESTRO STA RT GETTING STA RT E D . [. . . ] Color coded connect lines provide a visual image of the 4048A routing scheme. 7. 3f HPF/LPF Bandpass or crossover functions on the 4048A are available only on the eight output channels. Every channel's crossover consists of a high pass filter (HPF) and a low pass filter (LPF), along with the frequencies and filter types used. Each output's crossover section is essentially a bandpass filter, making it necessary for the user to map out ahead of time which outputs will be used for the various frequency bands, and set the overlapping filter frequencies and types accordingly. Note: The HPF determines the lower frequency limit of the signal, while the LPF determines the upper frequency limit. The frequency range for the high pass filter (HPF) is from 19. 7Hz to 21. 9kHz, with an option to turn the filter off at the low end of the frequency selection. The low pass filter (LPF) offers the same frequency range, with the "off" option at the high end of the frequency selection. There are eight types of filters available in the crossover section, each suited to a specific preference or purpose. The slope of each filter type is defined by the first characters in the filter type, 12dB, 18dB, or 24dB per octave. The steeper the slope, the more abruptly the "edges" of the pass band will drop off. There is no best filter slope for every application, so experiment to see which one sounds most pleasing in a specific system. The pre-loaded presets all use 24dB/octave filters in the crossover section, but of course they can be changed to suit the application. In addition to the frequency and slope, crossover filters can be selected as having Butterworth, Bessel, or Linkwitz-Riley response. These refer to the shape of a filter's slope at the cut-off frequency, affecting the way two adjacent pass bands interact at the crossover point. 24dB/octave Linkwitz-Riley filters produce a flat transition through the crossover region, assuming both overlapping filters are set to the same frequency, slope, and response type. 24dB/ oct Linkwitz-Riley filters are the industry standard, the easiest to use, and the filter type recommended by Altec Lansing. Other filter types are available, but may require polarity switching or other adjustments for proper results. The following paragraphs offer a summary of the three filter types as used in the 4048A processor. 12 Operating Manual-4048A digital signal processor Butterworth Butterworth filters individually are always -3dB at the displayed crossover frequency and are used because they have a "maximally flat" passband and sharpest transition to the stopband. When a Butterworth HPF and LPF of the same crossover frequency are summed, the combined response is always +3dB. With 12dB per octave Butterworth crossover filters, one of the outputs must be inverted or else the combined response will result in a large notch at the crossover frequency. Bessel These filters, as implemented on the 4048A, are always -3dB at the displayed crossover frequency. Bessel filters are used because they have a maximally flat group delay. Stated another way, Bessel filters have the most linear phase response. [. . . ] Monitor cables and Null Modem cables will not work. 16 Operating Manual-4048A digital signal processor 2. ) Use a valid PC serial port. You must use a serial port that is not opened to any other application, such as a mouse, modem, or another program. To verify that the port exists look in: Control Panel - System - Device Manager - Ports. While you're there, make sure that the port has no warnings or conflicts. [. . . ]