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Low shelf on iPad
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Joined: 03/07/2012 19:28:18
Messages: 31
Location: Toronto, Canada


I am new to ‘sound’ and still learning the 24.4.2 board at our church.

I love the new 24.4.2 board and all it’s capabilities, but we don’t yet have the hardware to be able to control it using the iPad (and it is very probable that the hardware will never materialize - unfortunately!)

However, even though there is no iPad connectivity, I have still found the iPad app to be very useful as a visual tutorial to teach me how each parameter affects the sound.

I do have a question about the low shelf. On the iPad it looks like what I would expect a low shelf to look like if I set it like this:

GAIN: -15.0 dB
FREQ: 150.5 Hz
Q: 0.46

However, if I want to get rid of more lows by changing the Q to to 4.0, a huge boost appears around 230 Hz on the iPad graphic.

Does that huge boost actually happen on the 24.4.2 board with these settings - or is that just a visual graphic glitch on the iPad?

Thanks, Presonus forum community!

iMac - Mountain Lion, iPad 2, Airport Extreme
Presonus Studio One 2 Professional
Apollo Quad and UAD plugins
StudioLive 24.4.2 at church


Joined: 09/08/2011 07:20:38
Messages: 22

Yeah! I just noticed that this past Sunday night while mixing on the iPad. I'll be waiting for a response on this myself.

Joined: 28/07/2010 23:56:13
Messages: 3002

I can't say definitively, but it is entirely possible that the "hump" is an artifact of the filter/algorithm, and not just a visual glitch -- that the visual you see reflects what is actually going on when you alter the Q. Filters (especially very steep ones) have a tendency to create a hump in the response curve. The steeper the slope, the bigger the hump. Maybe Mike Rivers or a PreSonus lurker can confirm or contradict.
Field Kit:
MacBook Pro 9.2 i5 2.5 GHz, 8GB RAM,
OS 10.8.5;
A & H Qu-16, AB1818VSL, Alesis IO14 / IO26,
PreSonus S1 v2.6.2.25990, Boom Recorder 8.3.2

Studio Kit:
iMac 11.3, i7 (Quad) 2.93GHz, 8 GB RAM,
OS 10.9.3,
M-Audio FW1814, PreSonus Faderport,
PreSonus S1 Pro

Joined: 28/07/2010 15:44:52
Messages: 2247

Has anyone thought to actually test it with a frequency sweep through the console? Then you'd know.

Q isn't really a conventional way of stating rolloff of a shelf. It's a measure of bandwidth, and how do you determine bandwidth when there's only one point on the curve that's 3 dB down from the reference?

A Q of 4, if it was a peak or dip, would be a bandwidth of 1/3 octave. A Q of 0.46 is a bandwidth of about 2.5 octaves. Maybe they mean that the slope is that of one side of a 1/3 octave or 2.5 octave bandwidth filter if it was a filter with a bandwidth.

Back in the day when "British EQ" was an endearing term describing a console, some people liked the response of an inductor-capacitor (LC) filter with a resonant peak just above cutoff. This sort of filter is still popular with synthesizers because that bump before the cut gives the sense that the lows (or highs) aren't cut as much as they actually are.
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"It's much easier to look for a magic solution than it is to adapt to reality." - Allan Sloan
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