Topic: Using attenuators

[SClassical]

Hi,
I'm planning to record using my V3 line out to my MR-1 and coax to my MT at the same time. The line out of my V3 is VERY hot and when I tried using it with my MR-1 it is not possible to record anything due this problem. I know I can reduce the gain setting in my MR-1 but I want to keep it at gain zero. My question is if I use this:

http://cgi.ebay.com/HOSA-ATT-448-Input-Attenuator-XLR-M-to-XLR-F-NEW_W0QQitemZ260104702942QQihZ016QQcategoryZ23783QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Would the quality of my sound recording be affected? Does an attenuator only reduce the vol or does it also alter the sound quality?

I hope someone knows the answer to my question.

[gratefulphish]

If you are running the V3 as an analog pre only, you need to keep the levels on the V3 lower. When using it analog out, you should only be flickering the first amber, not filling them up, much less hitting clip.  This should bring your signal level down to the appropriate level for the rest of the gear.  The attenuators do their job, across the entire spectrum, just reducing the overall level by the stated db reduction.  There are fixed 10, 20 and others, and some variable switch models.  Try the lower V3 level first, and then see whether you need any attenuating.  Normally, the attenuators would go between the mics and a pre, and not after.  Hope this helps.

[Todd R]

Attenuators are just a resistive circuit.  It generally is considered something you should avoid, but you may not realistically have an option.  Basically anything you run your signal through will color the sound to some extent.  Using attenuators are no different, but you may not really be able to discern any difference at all, so you don't need to avoid them at all costs.

As to where to run the V3, this notion you should run it analog out so you are just hitting the first amber lights drives me nuts.  It is just a rule of thumb someone came up with for their particular gear, and now everyone seems to spread it around like gospel (no offense gratefulphish, just wanted to set the record straight).  The first amber light really has nothing to do with anything in the grand scheme of things.

The V3 will absolutely, positively not overload on the analog outputs if run above the first amber -- it'll be fine all the way up to clipping (but not at the clip point).  That is, the V3 in and of itself is perfectly fine being run very hot on the analog outputs.  I run mine all the time with it going all the way up to >-1db (all three amber lights) going analog in to my 722 -- no problem at all. 

The issue isn't the V3 overloading on its analog outputs, the problem is overloading the analog inputs of the downstream gear.  And the V3 puts out a very hot signal -- +25dbu max.  My 722 can take +25dbu, so it is no issue running the V3 as hot as I'd like.  If your gear takes a lower maximum input before overloading (brickwalling), then you need to reduce the output of the V3, simple as that.

For instance, my MT can only take a +3.8dbu signal at a maximum.  The V3 puts out +4dbu when just the first 2 green LEDs are lit.  So if I even hit the second green LED on the V3 going analog out to the MT, I will overload my MT.  The first amber light people talk about so much correlates to an output of +16dbu on the V3's analog outputs.  So with just hitting the first amber on my V3, I will overload the crap out of my MT.

For your specific case of the MR-1, Korg lists the maximum input level as +6dbV.  +6dbV is the same as about +8dbu, so the max the MR-1 is +8dbu.  The V3 puts out +10dbu when the third green LED is lit, so you'd need to run the V3 so you light up no more than the first 2 green LEDs.  If you hit the third green LED, you're overloading your MR-1, with even worse overloading if you hit the 4th green LED.  If you hit that first amber LED on the V3, you'll again (like the case of the MT) be overloading the crap out of your MR-1.

I really don't see running your V3 so low that you really can't see what's going on with the meters, so I'd really suggest getting a pair of attenuators.  -20db attenuators should do it.

[I will say that what I've said about the V3 and MR-1 is based on published specs, not trying things.  But I can say for sure that you can run the V3 much hotter than the first amber without any problem when running into the 722.  And the first amber is way too hot for running the V3 into the MT.]

Sorry for the long-winded post, but I'd really like to totally get rid of this notion that running the V3 at the first amber LED is the right place to be running it when running analog out.

[SClassical]

Thanks for your messages! It really helped...

Since I will be running my MT (via digital coax from the V3) at the same time as my MR-1 (via line-in), I cannot turn the gain too low - upto the 2nd green light on the V3 to prevent brickwalling my MR-1. Or I'll end up with very low levels in my MT, which I'll need to increase post recording in an audio editing program.

Most people put the attenuators between the mics and preamp (in my case between the mics and V3). If I get a -20dB attenuator as ToddR suggested do I put it between the V3 and MR-1 so it doesn't affect the signal going to my MT (my MT signal it will get affected if I put the attenuator between the mics and V3).

(PS I'll like to keep my gain of my MR-1 zero because if I lower it to -20dB I'll get brickwalling - so I'll need to lower the signal going into my MR-1 without affecting the signal going into my MT).

So ToddR I guess you're saying I should get a -20 dB attenuator and put it between my V3 and MR-1. And if the peak on the V3 doesn't reach the red light my recordings from my MR-1 and MT should be fine?

Thanks again!

[Todd R]

Yep, that's it -- place the attenuators between the V3 and the MR-1.

If you use -20db attenuators, you can run the V3 signal as hot as you like (short of clipping) and you'll be fine.  The V3 puts out +25dbu max, less the 20db from the attenuators, so your MR-1 will see +5dbu max.  Since it can take up to +8dbu, you'll be fine.

[gratefulphish]

ToddR, yes I was repeating certain gospel about where to set the V3 for analog out.  I have a 722 on the way, so I appreciate your input (no pun intended).  I have heard that there is a unity setting on the 722, but have not had time to search the threads for more info.  I would appreciate any V3>722 tips and tricks that you may want to offer.  Sorry for the threadjack.

[SClassical]

ToddR, yes I was repeating certain gospel about where to set the V3 for analog out.  I have a 722 on the way, so I appreciate your input (no pun intended).  I have heard that there is a unity setting on the 722, but have not had time to search the threads for more info.  I would appreciate any V3>722 tips and tricks that you may want to offer.  Sorry for the threadjack.

gratefulphish, maybe you should read these:

http://taperssection.com/index.php/topic,80074.0.html

http://taperssection.com/index.php/topic,81297.0.html

[landshark]

Todd R -

Freakin awesome stuff, man!  I've been having similar issues with my MR-1 and purchased some attenuators.  Great write-up, and helps fill in the gaps.  Thanks!!!

Mike

[Church-Audio]

Hi,
I'm planning to record using my V3 line out to my MR-1 and coax to my MT at the same time. The line out of my V3 is VERY hot and when I tried using it with my MR-1 it is not possible to record anything due this problem. I know I can reduce the gain setting in my MR-1 but I want to keep it at gain zero. My question is if I use this:

http://cgi.ebay.com/HOSA-ATT-448-Input-Attenuator-XLR-M-to-XLR-F-NEW_W0QQitemZ260104702942QQihZ016QQcategoryZ23783QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

Would the quality of my sound recording be affected? Does an attenuator only reduce the vol or does it also alter the sound quality?

I hope someone knows the answer to my question.

Good attenuators that are designed around your input impedance and output impedance.  Properly designed they will have little effect on your performance of your gear. However the more you attenuate the more your signal to noise ratio gets out of whack. Some attenuators will effect high frequency response but we are talking about -.5 db to 1db  I have always felt it's better to use an analog attenuation then a digital one. Also all of the best recording consoles in the world have some kind of mic pad available at the input, this proves my point about well designed attenuation. So its important to understand what impedance the attenuator was designed for and use the correct one for the correct input impedance / output impedence to get the best possible results and to make sure that you use it as little as possible, this often means using one that is "custom made" for your application in most cases.
I think good attenuator or pad should have 5 db increments. This -10 -20 -30 is really heavy attenuation that more often then not leads to increased noise floor.

That's my two cents.

Chris

[gratefulphish]

ToddR, yes I was repeating certain gospel about where to set the V3 for analog out.  I have a 722 on the way, so I appreciate your input (no pun intended).  I have heard that there is a unity setting on the 722, but have not had time to search the threads for more info.  I would appreciate any V3>722 tips and tricks that you may want to offer.  Sorry for the threadjack.

gratefulphish, maybe you should read these:

http://taperssection.com/index.php/topic,80074.0.html

http://taperssection.com/index.php/topic,81297.0.html

Thanks.  I have read both threads, but there seems to be somewhat of a difference of opinion (on this board, can you believe it?) about whether to run the 722 at -5db, and run the V3 hot, or run the 722 at O db and then run the V3 lower.  Any real pluses or minuses to one vs. the other?  Preferences?  Once again thanks for the enless help and +T.

[Church-Audio]

ToddR, yes I was repeating certain gospel about where to set the V3 for analog out.  I have a 722 on the way, so I appreciate your input (no pun intended).  I have heard that there is a unity setting on the 722, but have not had time to search the threads for more info.  I would appreciate any V3>722 tips and tricks that you may want to offer.  Sorry for the threadjack.

gratefulphish, maybe you should read these:

http://taperssection.com/index.php/topic,80074.0.html

http://taperssection.com/index.php/topic,81297.0.html

Thanks.  I have read both threads, but there seems to be somewhat of a difference of opinion (on this board, can you believe it?) about whether to run the 722 at -5db, and run the V3 hot, or run the 722 at O db and then run the V3 lower.  Any real pluses or minuses to one vs. the other?  Preferences?  Once again thanks for the enless help and +T.

I wish I could help you there. But one bit of advice I can give you is talk to a technician at the company that makes your product. They should know what is best for your unit. I think that running hot when it comes to digital is not really a good idea, I feel that having a good signal to noise ratio is much more important then running anything to hot. In the old analog days we ran things hot to get that nice tape compression. But now with digital its not a matter of how hot to run levels but more so how much do we have to boost on the other end. The less boosting the better but, I have always felt when your recording a live show its always better to be conservative with levels then aggressive.

Chris

[Todd R]

Well, having said that the 722 can take the full-blown analog signal of the V3, I'd venture to say it is better to run the 722 at 0db, and reduce the output of the V3.

From my standpoint, I'm lazy and want to reduce the amount of time I spend post-processing.  So I run the V3 hot and run the 722 at -5db.  This since I run V3 (digital)> recorder (either H120 or MT) at 16bits and run V3(analog) > 722 at 24 bits.  If I run the V3 hot and calibrate the V3 to the 722 with the 722 set to -5db, then I can just directly use both the 16 bit and 24 bit recordings, without needing to boost my levels in post.  If I ran the 722 at 0db gain and ran the V3 lower, then at the least I'd need to boost my V3>MT (16 bit) recording by (at least) 5db.

Such laziness aside, from a pure sound standpoint, running the 722 at 0db gain would make more sense than adding a more gain to the signal than necessary at the V3 and then reducing it at the 722 by running at -5db.

[Roving Sign]

Such laziness aside, from a pure sound standpoint, running the 722 at 0db gain would make more sense than adding a more gain to the signal than necessary at the V3 and then reducing it at the 722 by running at -5db.

But doesnt that lower the V3 signal to noise ratio? It just seems like you would be wanting to use the v3 to its full analog potential - - -without regard for any recorder - - -first...and then go from there...

Totally offhand remark - but has anyone just split the signal at the mics and run each (v3 / 722) to their full potential?

Not sure what the penalty is for mic splitting - perhaps that would be too much...

Ok - sorry to jump in - I dont have any of said gear - but I read these threads and sometimes I just have to ask...

[SparkE!]

Such laziness aside, from a pure sound standpoint, running the 722 at 0db gain would make more sense than adding a more gain to the signal than necessary at the V3 and then reducing it at the 722 by running at -5db.

But doesnt that lower the V3 signal to noise ratio? It just seems like you would be wanting to use the v3 to its full analog potential - - -without regard for any recorder - - -first...and then go from there...

Totally offhand remark - but has anyone just split the signal at the mics and run each (v3 / 722) to their full potential?

Not sure what the penalty is for mic splitting - perhaps that would be too much...

Ok - sorry to jump in - I dont have any of said gear - but I read these threads and sometimes I just have to ask...

You only have to worry about attenuators hurting the S/N when the signal is pretty small.  By the time you're up around 100 mV or more (consumer gear line level), you're not going to have noticeable problems with S/N degradation due to an attenuator.  Also, as long as your attenuator is purely resistive and you are operating into an input whose impedance is purely resistive, it does not cause any filtering so you don't have to worry about shaping the spectrum.  From a purely mathematical point of view, you get less degradation in S/N when you use a larger signal input, but it may not be worth the tradeoff you take in harmonic distortion when you produce that larger signal.  The smaller the impedance of your attenuator, the less thermal noise it adds.  For instance, a 3k resistor at room temperature produces about 1 uV rms of noise voltage in a 20 kHz bandwidth.  A 300 ohm resistor only produces about 1/3 that much noise voltage in the same bandwidth.  A 100 mV signal is 110 dB above that level, so you can give up 20 dB of signal attenuation and still have a 90 dB S/N at the output of the attenuator.

[SparkE!]

I should also point out that if you use a transformer to change signal levels, you take less of a hit in S/N because the series resistance of either winding is going to be very small.  The tradeoff is that you end up adding some filtering because the passband of the transformer is not going to be perfectly flat.  It's a matter of whether you prefer to add noise or color.

[gratefulphish]

Well, having said that the 722 can take the full-blown analog signal of the V3, I'd venture to say it is better to run the 722 at 0db, and reduce the output of the V3.

From my standpoint, I'm lazy and want to reduce the amount of time I spend post-processing.  So I run the V3 hot and run the 722 at -5db.  This since I run V3 (digital)> recorder (either H120 or MT) at 16bits and run V3(analog) > 722 at 24 bits.  If I run the V3 hot and calibrate the V3 to the 722 with the 722 set to -5db, then I can just directly use both the 16 bit and 24 bit recordings, without needing to boost my levels in post.  If I ran the 722 at 0db gain and ran the V3 lower, then at the least I'd need to boost my V3>MT (16 bit) recording by (at least) 5db.

Such laziness aside, from a pure sound standpoint, running the 722 at 0db gain would make more sense than adding a more gain to the signal than necessary at the V3 and then reducing it at the 722 by running at -5db.

Well, you opened up a whole new door of ideas with this post.  With the R-4 Pro, it was either 16 or 24 bit.  Now, as you have pointed out, I can run the 722 at 24, and the MT at 16, when I am not otherwise running four tracks, and just give the band the CF card at the end.  Might make life much easier that doing all the post myself. Thanks again.

[SClassical]

If I want to make a 10dB pad cable do I put a 2.2K resistor between the tip on one end to the other and another 2.2K resistor between the the ring of one end to other, then bridge the tip and the ring with another 2.2K resistor? (Using 1/8" TRS connectors both ends).

[SparkE!]

If I want to make a 10dB pad cable do I put a 2.2K resistor between the tip on one end to the other and another 2.2K resistor between the the ring of one end to other, then bridge the tip and the ring with another 2.2K resistor? (Using 1/8" TRS connectors both ends).

No. Doing that just gives you a bunch of crosstalk between the channels.

If you know the input impedance of the device into which you are feeding the signal (call it Rin) and that input impedance is can be considered to be purely resistive in the passband of that input, then you just need series resistors in both the left and right channel signal paths whose values are both equal to approximately 2.162 Rin.

[it-goes-to-eleven]

It would be interesting to do some live comps that focus specifically on the audio impact of attenuators and whether they degrade sound. I recently picked up an eaa psp2 and it runs pretty hot for loud shows so I'll either be running the pad on the mics or the 722 at -6 or both.

And as far as the 722 is concerned, in conversations with Justin at sound devices he has discouraged running it super hot. In general I think my recordings where I peak at -12 to -8 are better than those where I ran closer to 0. I think the RMS avg is also a factor (beyond mere peak) since it tends to vary greatly with type of material.

[gratefulphish]

And as far as the 722 is concerned, in conversations with Justin at sound devices he has discouraged running it super hot.

What level did he consider to be "super hot?"

[it-goes-to-eleven]

He generally encouraged recording to a lower level, maybe -12 or so.  Though the focus of the discussion wasn't so much on audio quality as you approach 0.

I had reported some problems with distortion if the 7xx clipped while the bass roll off was enabled.  So that is what lead to the discussion.  At quiet shows in tape from seat situations, a loud clapper in the next seat can really blow your levels..

I think we can only settle this 'optimal level' question through some good comps.

[gratefulphish]

I had thought from reading numerous threads here, that the additional dynamic range added by 24 bit recording allowed us to back off levels from trying to peak close to 0db, and that -6db was considered adequate in a 24 bit setting.  But -12db seems to be wasting a lot of potential range, and since I rarely tape anything close to quiet, I am not worried about the potential of a loud clapper blowing my levels.  But in any case, that still seems like a lot of empty space.

BTW, which rolloff settings were you using, and what were the issues.  I had been considering using the 722 rolloff vs. the rolloffs on the Neumanns, as in almost all indoor settings, I have found them necessary for decent recordings.  I also have the option of using the V3's rolloffs as well.  Anybody ever compare the various rolloffs?   This could be a new thread.

[it-goes-to-eleven]

I think you'd be better off using the rolloff on the mic but you should really do your own tests. I'd expect the 7xx roll off has been improved but don't know the current status. Running it at all was somewhat of an experiment and I haven't touched it since I was burned. I was using the mildest rolloff setting.