Table of Contents
Advertisement
Note: Not all the values in the boxes are used for all filters. For example, the slope, dB/oct, and
Q, are not used for HPBW4, etc. If you change a value and there is no change in the graph, that
parameter is not used. Also, the High Pass Shelf and Low Pass Shelf filters are not "real" shelving
filters but special target filters. "Real" low pass and high pass shelving filters have roll-offs that are
multiples of 6 dB /oct. The special target filters can have an arbitrary roll off. For an example, in
post-production, near-field monitors used for editing may require a 3-dB/oct roll-off above 4 kHz so
the sound translates better to the dubbing stage. Although a 3 dB target curve can be constructed
with conventional filters, it may take 6 or more separate filters and a lot of experimentation to get
the target curve you want. However, with the special target shelf filters, you can enter -3 dB directly
without all the fuss and it is much easier.
Target Scale Low and High Freq – the software uses the frequencies between these values to
calculate the avg. microphone level, which is used to adjust the target curve, so it "floats" with the
drive level. These frequencies are selected to be in a "flattest" portion of the measured curve.
The default range for satellite speakers is 500 Hz to 2.5 kHz. while for subwoofers the default
range is 40Hz to 80 Hz. However these values can be modified to suit your particular
circumstances.
Low and High Target Freq – these two frequencies restrict the range of the optimizer. Any
frequencies outside this range are excluded from the optimization process, allowing you to limit the
range of optimization. Any filter, either graphic EQ, or a user assigned filter, outside of this range
would not be altered by the optimization process. For example, suppose you wanted to only
correct the low frequency portion of the main speakers from say 40 to 200 Hz. In that case, you
would input 40 Hz in the low target frequency and in 200 Hz in the high target frequency. When the
speaker is optimized, any one 3rd octave filters outside this range would not be modified, nor with
any user assigned filter outside this range be modified.
Gate time in milliseconds - this value sets how much of the impulse response is used to calculate
the frequency response. The AMC SRO program uses a Blackman – Harris window function on
the impulse response when calculating frequency response. The gate time determines how much
of the low frequency content of the impulse response to include in calculating frequency response.
The lower the frequency you want to measure, the longer the gate time needs to be so it includes
more of the low frequency energy that's contained in the impulse response.
Page 31
Advertisement
Table of Contents
