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Why I should always use a QSC Processor with
QSC WideLine Loudspeakers
The question comes up time and again – why is QSC telling me I should buy a QSC processor with their
WideLine family of loudspeakers, when I already use a perfectly good DSP processor from Brand “X”.
In this document we hope to provide three compelling arguments why you should ALWAYS use a QSC
processor with your QSC WideLine array (including ILA). Ultimately the decision is yours, but it is our
hope that after reading this document, common sense will prevail!
1/ EASE OF USE:
The SC28 has been designed with a simple Array‐wizard function that allows the user to quickly key in a
few “physical” parameters (number of boxes, amps used etc). This programming process takes on
average about 5 minutes, at the end of which you will have authorized factory tunings for your array,
with an extremely neutral power response. We have made every effort to provide a turnkey solution!
By comparison, most drag n’ drop DSP boxes can take hours to program, and without understanding the
very complex nature of Line Array interaction in the vertical domain, you would likely spend many hours
trying to make the array sound as even close to the way an SC28 sounds after only 5 minutes!
The simple fact is that the cost of an SC28 as a percentage of the total system cost (amps, speakers,
array frames etc) is almost negligible, however the savings in programming time and user frustration
makes it an invaluable investment. It is likely that the on‐site labor required to achieve even marginally
acceptable results would probably exceed the cost of an SC28 anyway, so it only makes sense to
minimize your onsite labor costs.
2/ INTRINSIC CORRECTION™: The WideLine family of products (including ILA) feature a patented Diffraction Slot waveguide which produces an industry‐best “140 degree” horizontal coverage. However like ALL waveguides, this particular type of waveguide requires its own unique corrective EQ settings. The SC28 employs extensive FIR filtering to achieve an extremely neutral power response (see Figure 1), which we refer to
as Intrinsic Correction™. This process involves numerous lab measurements that have been spatially
averaged. More details about the Intrinsic Correction™ process can be found at the following link; http://www.qscaudio.com/products/dsp/SC28/intrinsic_correction_whitepaper_2007.pdf
Figure 1. Intrinsic Correction™ for ILA. Folks ‐ do not attempt this at home!
It is also worth noting that trying to replicate Intrinsic Correction™ inside a competitors DSP box would take weeks of laboratory work, due to the difference in DSP algorithms (see below), and quite honestly most low to medium‐cost DSP boxes do not even have the necessary FIR filters or horsepower available for the task!
If you have any doubts about whether Intrinsic Correction™ actually works, look no further than QSC’s
popular K, KW & KLA series of loudspeakers.
3/ NO TWO DSP BRANDS WORK THE SAME:
Now we get to the real crux of the matter. No two DSP brands work the same! Period! Therefore to
make them “sound” even moderately similar can take hours & hours of manipulation in the lab – and
often that process just comes down to pure trial and error. The quality difference in AD/DA convertors
alone can be a factor in tonal variance, however it’s really under the hood in the DSP engine (where
those little 1’s and 0’s are told what to do) that the real differences occur! Each set of instructions given
to the DSP engine is called an algorithm, and every manufacturer uses their own custom algorithms that
are completely different.
In the first example (figure 2) we have illustrated the difference between DSP brand X (blue) and DSP
brand Y (red). Despite inserting the EXACT same Crossover parameters (24db/octave Bessel filter @
1.18kHz), there is still an almost 6dB variation at the crossover point due to the different algorithms.
Furthermore Brand X has a net group delay of 2.9mS from its crossover filter, whereas Brand Y only has
a group delay of 1.3mS. This time / phase variation is colossal ‐ what occurs in the time domain can
have even more disastrous consequences than what occurs in the frequency domain (especially with
multiple element Line Arrays), and yet the time “smear” that results from these different group delays is
almost never considered when swapping out DSP brands.
Needless to say these two DSP boxes sounded completely different even though the parameter values
entered were identical!
Figure 2: DSP Brand X versus DSP Brand Y – using the exact same crossover parameters
‐2.7dB
‐8.2dB
In the next example an engineering team spent a long time in the lab trying to replicate a simple bell EQ
filter (‐6dB @ 500Hz) of two DSP brands to look exactly the same, and eventually they were able to get
them to within 1dB of each other. This was achieved by painstakingly overlaying the transfer functions
directly from the output of each DSP processor, but in the process ignoring any group delay variances
that were occurring behind the scenes.
The reason this process took so long was simply because each brand has different resolutions within the
instruction sets of their algorithms, and although the shape of the EQ curve looks almost similar, the
parameters applied ended up being completely different (see figure 3);
Needless to say these two DSP boxes also sounded completely different, even after hours in the lab
trying to match them up!
Figure 3: DSP Brand X versus DSP Brand Y – laboriously trying to replicate EQ curves
WHAT IF I NEED MORE INPUTS?
One of the most common reasons we hear for NOT using an SC28 is because it only has 2 inputs, and in some situations extra I/O is required to run separately processed Sub‐Aux feeds or Fill speakers. The SC28 was designed to do one thing, but it does that extremely well – that is to dynamically process a WideLine array. If you desire to individually process your subwoofers with a separate DSP box then we happily encourage that.
Brand X - 0.250 octave (Q = 4.00), 500 Hz, -6 dB (orange) Brand Y - 0.293 octave (Q = 3.41), 500 Hz, -6 dB (blue)
Brand X ‐ 0.250 octave (Q = 4.00), 500 Hz, ‐6 dB (red)
Brand Y ‐ 0.293 octave (Q = 3.41), 500 Hz, ‐6 dB (blue)
The simple reality is that Sub‐band processing is far less complex because of the longer wavelengths involved. By comparison the MF/HF processing is extremely complex due to diffractions & reflections of
the shorter wavelengths, and this is where Intrinsic Correction™ takes place.
SUMMARY:
If you decide to use a competitor’s DSP box on any WideLine system, please do not expect the array to
perform to its optimum level, even with the exact same parameters entered. At best you might only
ever achieve a “close approximation” of the factory voicings, and even then only after hours (and in
some cases after days) of painstaking measurements and DSP adjustments.
On request QSC can disclose the DSP parameter values that we input into the SC28, but please
understand that unless your DSP box uses the exact same algorithm instructions as ours (which it won’t),
the results will ALWAYS sound different, your customer may be disappointed with the results, and QSC
will be unable to provide the high level of application support that we typically pride ourselves on.
However if you purchase the WideLine system WITH an SC28 processor, your programming time will be
reduced to approximately 5 minutes, and the system will always sound great ‐ out of the box ‐ every
time, due to the Intrinsic Correction and Array‐Wizard functionality which are simply not available on
competitors products.
© 2011 QSC Audio Products, LLC. All rights reserved.
TMG-6/20/11
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