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input pad for monitors Utility Plugins
Old 10th September 2011
  #1
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input pad for monitors

I calibrate my monitors to 83db with an SPL meter and pink noise. This is way loud in my little room, so I've been dragging the master fader in the DSP down 12-14db to get a comfortable listening level for mixing. Being a relative digital noob, I did not know that lowering the volume digitally reduces the amount of bits I hear.

After researching volume controls, attenuators, and such, I've decided all I really need is a 12-14db pad between my interface and monitors. The math for such a thing is simple except I don't know the output impedance of the Echo A4 (not in the specs) or the input impedance of the Yamaha HS50Ms.

It can't be rocket surgery because there are several units you can just plug and play like a Nano Patch or Atty.

Or there some "safe" values for the input and output resistors, or a relatively simple way to measure them?

Thanks, guys.
Old 11th September 2011
  #2
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My friend Rick Chinn has posted this page:

Uneeda Audio - Build your own attenuator pads

If the monitors have unbalanced inputs, the second pad values in the chart at the bottom of the web page will work. If the circuit is balanced, use a "U" pad with 5.1K resistors for the two series legs, and 3.6K for the shunt (R2 in Rick's "U" pad schematic). For best results (minimizing any effects of cable/wire capacitance), install the pad at the monitor end of the cable.

Also, you can "diddle" the value of R2 to "tune" the amount of attenuation. Lower value of R2 provides MORE attenuation.

Best,

Bri
Old 11th September 2011
  #3
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A few years ago I had the same problem for my 5.1 monitoring system and my cheap solution was to create a box that uses that U attenuator circuit. The commercial versions were just too expensive for my budget. However all my lines are balanced and don't exceed 6 meters so it works quite transparently. The version I used was this basic circuit because it pretty much matched my impedance in and out (the link doesn't bring you to the page anymore, scroll down to the bottom of the index on that page and click on "Pass Attenuator", or search for it on that page).

I replaced the resistor across the balanced lines with a cermet trimmers so I could calibrate the levels. The advantage of this too is that you only have to worry about matching the 2 input resistors (I matched them to at least .1%). I also included 4 different groups: 3 calibrated levels for different program materials (I used Bob Katz's recommended levels for cinema, music and broadcast); for the fourth I used a 6 channel audio pot I found on eBay for when I'm composing; I wouldn't mix with that pot because I don't trust the channel-to-channel accuracy.

While I was at it I also put relay mutes that short the balanced lines for F/C/LFE/Rears and a master mute that kills all channels in case of emergency. All that switching is just mickey-mouse logic with diodes and switches.

It was a hell of a lot of point-to-point wiring, but it's been working reliably for several years. But if you're only doing stereo, it would be pretty quick to put together.
Old 11th September 2011
  #4
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A good point re. left/right attenuation matching. Rick's examples use standard 5% tolerance resistors, but L-R level matching accuracy will be improved by using the "closest" values with 1% tolerance resistors if the powered speakers don''t have input level adjustment/tweaker pots.

Adding a trimmer pot in the R2 position ( a 10 or 20-turn pot) will allow ultimate "fine tuning", but you will need an accurate AC Volt meter and an input test signal in order to "tune" the levels of the tweaker pots in the pads.

The "U" and "L" example attenuators at Rick's page should work with just about any system, since they are "bridging" with over 10K input impedance, and a relatively low output impedance.....suitable for this application.

Best,

Bri
Old 11th September 2011
  #5
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Thanks, gents!

Brian, How close is close? My cables are only 8' max from the patchbay to the monitors.
Old 11th September 2011
  #6
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I totally agree that the level is too high for comfort, I use a stepped attenuator and only check my work at that level.

If you are building your own pads, I got the high quality components for my attenuator at Michael Percy Audio.

But I don't understand the approach or what you will gain by it. Can't you control the output levels from your Echo audio applet?

The ATTY probably doesn't have the precision for this work, though I would check with Pete about that. I have the single channel ATTY in my toolbox, handy device. The Suzy from RME was touted as having better pots, I don't know.

Besides Ricks handy page, Fred Forssell offers schematics that will use his op amps which can be adapted for this purpose; there are also kits/pieces/parts for passive attenuators from DACT and Goldpoint which are affordable but limited in resolution.
Old 11th September 2011
  #7
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Quote:
Originally Posted by [email protected] View Post
I totally agree that the level is too high for comfort, I use a stepped attenuator and only check my work at that level.

If you are building your own pads, I got the high quality components for my attenuator at Michael Percy Audio.

But I don't understand the approach or what you will gain by it. Can't you control the output levels from your Echo audio applet?

The ATTY probably doesn't have the precision for this work, though I would check with Pete about that. I have the single channel ATTY in my toolbox, handy device. The Suzy from RME was touted as having better pots, I don't know.

Besides Ricks handy page, Fred Forssell offers schematics that will use his op amps which can be adapted for this purpose; there are also kits/pieces/parts for passive attenuators from DACT and Goldpoint which are affordable but limited in resolution.
It's my understanding that reducing volume in the DSP works by discarding information--cutting the number of bits used. Analogue attenuation is supposed to be more accurate.
Old 11th September 2011
  #8
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With only 8' of cable, a typical pad can be installed anywhere it is convenient.

Best,

Bri
Old 11th September 2011
  #9
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That's what I needed. Thank you, sir!
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