I see that the spec on the DSP-30 shows a bottom frequency of 20hz.
In questioning QSC, they say it goes beyond that.
In your experience, can you effectively go below 20hz and if so, any side effects?
Hi JimP, This is a fairly common trait to most of the DSP based EQ's on the market. The main thing you have to check with some is what sort of low frequency throughput the electronics have. In other words, when no filters are applied, how does it roll off the low end? All DSP based products will at some low frequency. There has been some documentation online, and Ilkka has tested quite a few units now; maybe he can chime in. Long ago I did contact QSC and then sent me an AudioPrecision measurement of the very low frequency extension, and going by memory, it was about -1dB to -2.5dB down at 10Hz. This is fine, especially if the device has shelving filters. You can download the software for most and look at the interface without having the physical EQ connected. You will find it is common that they simply limit the numerical input in the software. There are some issues that can come in with very low frequency filters, but most companies have done a plenty good job with the design such that taking a few measurements to adjust for what is really happening vs. what you expect makes it a non-issue. So far as actually applying and using the filters, you will see in the DSP-30 software that the very small graphic display does extend to 10Hz. All of the filters will have effects centered on the entered frequency, and will extend below 20Hz just fine. Shelving filters will greatly affect >20Hz, and often an additional PEQ in the 20-25Hz range can shape the exact effect. Another "trick" is that Bessel filters of 12-24dB are shallow in their initial roll off. This can be used in combo with a low shelving filter or even PEQ to produce an effective low corner that is well below 20Hz. One aid in setting up such filters where the display doesn't show them well down low is to scale them by a factor of 10. So move that 20Hz filter to 200Hz, and experiment with other filters also set above 200Hz so you can better see what is going on to 10Hz or below. Once you see a desireably shaped response, just enter the intended frequency of each filter by dividing by 10.
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