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Topic: Level mismatch solutions - fixed and variable attenuators

Level mismatch is a continuing topic on our forum and support line. The most often reported problem is that active monitors are far too sensitive. The low volume click and pop when turning a unit on/off turns into a quite loud one. A volume control pot then has a very limited operation area, and the master fader in TotalMix has to be lowered to below -20 dB constantly. This also raises concerns about reduced audio resolution. With such a level mismatch hum and noise can also become audible.

What needs to be done in such cases is to make the connected amplifier or speakers/active monitors as insensitive as possible. Ignore whatever the current setting print on the monitor says, choose one that makes them as low in volume as possible.

Some customers encounter situations where this is not enough. We heard of professional and very powerful active monitors using a reference level of +4 dBu, which seems to equal full output power. Setting an RME unit to -10 dBV, which equals +4 dBu at full output level, then again requires to lower TotalMix FX to far more than -20 dB to be able to work at a typical studio listening level - plus having all the above disadvantages/problems.

The solution here is to use passive damping between the RME interface and the amp/active monitor's input by a simple voltage divider, built of 2 (unbalanced) or three (balanced) resistors per channel. Do a Google search for 'line level audio attenuators' or just 'audio attenuators', and you will realize that this is not a RME problem, but a long time classic found everywhere - even in home HiFi. And this is also the reason that the web is not only full of examples on how to build such parts, including the part values and circuit diagrams, but why they are also available at reasonable prices in various models from various manufacturers.

If you don't want to waste your time with ordering parts, soldering, and drilling housings, here are two solutions that have been tested to work perfectly with RME devices:

For balanced outputs: JTS Mic attenuator MA-123, XLR to XLR, available for around 20 €, switchable attenuation of -10, -20 and -30 dB. Don't get confused with the term 'mic attenuator'. It works perfectly with line outputs. In fact it works even better as other 'line' solutions, because its impedance is high enough for the RME output stages to not cause distortion (1 kOhm), but very low for any following device (below 200 Ohm), which means there is no added low level noise and no high frequency rolloff caused by cable capacitance when plugged into the output of the RME device. Of course, cable influences can be ruled out completely even with higher impedance attenuators by plugging them directly into the amp/monitor's input jack - at the end of the cable.

For unbalanced outputs: IMG Line attenuator ILA-1020, RCA to RCA, switchable attenuation of -10, -15 and -20 dB. One pair is available for around 25 €. Note that these use much higher resistor values than the balanced ones, more than 10 kOhm input and around 1 kOhm output. Therefore they should be placed directly at the input of the receiving unit, not at the output of the sending one.

These are just two examples. There exist many other, like:

Balanced:
Hosa ATT448
Pro Co Max20
Audio-Technica AT8202
Shure A15AS

Unbalanced:
Rothwell RCA attenuators
Harrison Labs RCA Line level attenuators

Another way to solve the level mismatch is by adding a variable resistor (aka potentiometer) instead of the fixed ones. Put the pot into a desktop housing and you have a variable volume control. These are also very popular, examples:

SM Nano Patch +, also available from JBL
Palmer Monicon

They have a few advantages: volume controlled from your desktop, mute switch provided, also serves as format adapter as it provides XLR, TRS and small TRS stereo on input and output simultaneously. The current generation uses quad potentiometers, so work both balanced and in stereo, and are also automatically compatible to unbalanced operation. All passive!

Compared to the above fixed low impedance resistor solutions the variable ones have a technical disadvantage - they use pots with 10 kOhm resistance, 10 times as much as the 'mic' attenuators. Ideal they would use 1 kOhm pots, but maybe decided for higher values as some devices have much higher output impedances as RME units. With 10 kOhm and the pot in the middle position a series resistor of 5 kOhm is in the signal path, and a parallel one of 5 kOhm works as load. Depending on the used cables and input circuitry a slightly increased noise floor as well as a slight high frequency damping might occur. In real-world operation and usage user feedback is very positive when using these devices.


Background information:

RME interfaces and converters provide several, user adjustable output levels, from -10 dBV up to +24 dBu. Most devices support +19 du, +13 dBu and +4 dBu (aka -10 dBV). Some devices like the Babyface and Babyface Pro do not support different ref levels at their outputs, for example the BF Pro XLR outputs are fixed at +19 dBu. As explained in the manuals a digital fullscale level in -10 dBV setting does not equal -10 dBV, but +2 dBV, or coarsely +4 dBu. The reason is that analog equipment, especially mixing desks working with this reference level, offer a very high headroom - not astonishing, as the internal circuitry ist still running with +-15V, the same voltage that is used for +24 dBu output level stages. We therefore defined our -10 dBV setting with 12 dB of headroom.

The attenuation required in mismatch cases as described above is typically -20 dB.

Regards
Matthias Carstens
RME

Re: Level mismatch solutions - fixed and variable attenuators

Many thanks !

UFX+,ADI-2 Pro,XTC,RayDAT,RL906D,
Win7/Cub9, Supermicro X10SRi-F, E5-1650v3, Sonnet USB3-PRO-4PM-E

Re: Level mismatch solutions - fixed and variable attenuators

That is a great article...thank you.

Babyface Pro, UFX+ via Thunderbolt, Win 10, Cubase 9, Asus Z270 i7700k Guitarist-1961

4 (edited by Markk786 2017-08-13 14:43:35)

Re: Level mismatch solutions - fixed and variable attenuators

Thanks a lot....!!!
subchorionichematoma

Re: Level mismatch solutions - fixed and variable attenuators

MC wrote:

For balanced outputs: JTS Mic attenuator MA-123, XLR to XLR, available for around 20 €, switchable attenuation of -10, -20 and -30 dB.

Where to even get these? Thomann doesn't hold them, and Monacor seems to be way too slow to authorize new webstore accounts, they don't even allow to browse the shop without logging in (lame).

Any other solutions are more than twice expensive (Shure, AT, especially Hosa) so I'm not interested in them. This JTS seems like just the ticket, but googling around, it's hard to find ANY shops that hold them! What gives? hmm

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Re: Level mismatch solutions - fixed and variable attenuators

Geht's hier um Deutschland/Europa? Dann kann ich nur sagen schlecht gesucht. Amazon.de hat zwar aktuell nur einen, Conrad aber jede Menge für 18,90. Etc etc...

Regards
Matthias Carstens
RME

7 (edited by EvilDragon 2017-10-15 17:45:35)

Re: Level mismatch solutions - fixed and variable attenuators

Croatia here, so EU, yeah...

Saw it available at Conrad.de, but they don't ship to Croatia (no options to enter a Croatian address in their webshop checkout). They do have a Croatian website, but no MA-123 on it available to order, at all (not sure why!)... sad

Re: Level mismatch solutions - fixed and variable attenuators

Just send a mail to the Croatian Conrad site and ask for the Conrad.de item.

The same happens with the Conrad.be site. They just don't have every item listed. Usually, they"re happy to add anything and a while later it'll be listed too.

Re: Level mismatch solutions - fixed and variable attenuators

Thanks, I think I'm gonna do that smile

Re: Level mismatch solutions - fixed and variable attenuators

If you ever liked a (over) priced solution, but one that looks unmistakably cool and stilish, and runs smooth as melting butter, here is one I've been using since ever, for this very purpose: http://www.tcelectronic.com/level-pilot/.  I find it easier to grab than turning the BabyFace Pro dial-wheel in a hurry-up occurence: it's closer, it sticks out, you grab it even if blindfolded, and it's never assigned to the wrong pair of outputs, or inputs, ever.

My case was as typical as all others here: amp on full input level was way too loud to make any sense, and yes, it's not RME's fault, not in the least. It's an evergreen, classic audio topic, that's been on any schooldesk ever since, for students and teachers alike to deal with, and solve. Like MC correctly points out, correct as ever, there's cheaper and cheapest solutions that do the job great, for peanuts. In my instance, cheap is often seen as wrong, even when it works great, so to dispel any doubt, expensive just means assuringly good (if it works, at least).

Pot works great, and it's also fairly even between channels, and at modest rotation angles, too, which, in my view, justified and justifies the hefty price: if lowering the program to whisper-level volume makes channels uneven, that's what spoils the whole effort. With this one, it doesn't happen, balance stays true, and that's what counts here.

What I can't forgive the maker for, though, are the connectors, of a cheaper-than-cheapest sort: for the price it sells (on average street level), it might as well have had Neutrik XLR connectors soldered at the end of the cable, and with a proper color coding scheme, none of which has been provided by the manufacturer.

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Re: Level mismatch solutions - fixed and variable attenuators

I overlooked that one, thanks. Would be nice to know how much Ohms the pot in it has. Also ESI just announced the new MoCo

http://www.esi-audio.de/produkte/moco/

which is comparable to the mentioned NanoPatch and Monicon units, and (not mentioned) others like the Mackie Big Knob Passive, the Swissonic M-Control and whatever there might exist. The MoCo now has the biggest variety of I/O connectors (therefore serves as jack format converter very well) and all the buttons one could want. Its design might not fit everyone, though.

The desktop pot solution is giving extra features, but this review of the MoCo reminds German readers that those units do introduce level mismatches over the pot range, reduce channel separation a bit, and (due to the higher Ohm pot) even might introduce a  little noise:

https://www.bonedo.de/artikel/einzelans … -test.html

Something you won't see with the more simpler level attenuators and a digital volume control.

Regards
Matthias Carstens
RME

Re: Level mismatch solutions - fixed and variable attenuators

MC wrote:

I overlooked that one, thanks. Would be nice to know how much Ohms the pot in it has.

just looked it up on ggl, searched for "bourns pot resistance tc level pilot". search returned a funny salesforce page (helpdesk material, most likely from manufacturer) saying it's a 4*10k log one.

opened up the thing, peeped at the blue plastic box of the pot, stamped across is 410K, which sounds consistent to the .pdf datasheet shared by manufacturer when users ask for pot replacement.

so 10k it is, a 4-wires Bourns PTD 904 - 1020K-A103.

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Re: Level mismatch solutions - fixed and variable attenuators

Ok, I better not ask you about details of RME devices wink

Regards
Matthias Carstens
RME