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Offline eclark

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Limiters?
« on: November 28, 2011, 01:52:22 PM »
Just wondering if anyone here uses limiters on their Sound Devices devices (or others) so you don't overload the preamp. What about running a -10dB pad on your mics?

My gain is set to 1 which is very low, and my levels are high, sometimes clipping. Would like to get as much gain as possible, without having the levels clip.

My preamp has the following specs:

SD MixPre-D Limiter:
adjustable threshold, +6dBu to +18dBu, 20:1 ratio, 1mS attack, 500mS release
akg 460b + ck61 (-10db) > MixPre-D > Sony PCM M10

Offline kleiner Rainer

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Re: Limiters?
« Reply #1 on: November 28, 2011, 02:15:26 PM »
Hi eclark,

do I understand your post correct: you set the gain pot to the first white dot above zero?
If yes, then I know what to do:

switch to Line in! Its still transformer isolated (seems to  be an attenuator on Mic in). No external attenuator needed.


BTW I measured a level of 100mV at the mic input of my MixPre D when the mic gain was set to the first dot above zero, with the +4dB LED lit (last LED before red). When I switched to Line input, I could turn up the gain to max to get the same level display.

Hope that helps!

Greetings,

Rainer

recording steam trains since 1985

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Re: Limiters?
« Reply #2 on: November 28, 2011, 02:36:39 PM »
switch to Line in! Its still transformer isolated (seems to  be an attenuator on Mic in). No external attenuator needed.

This is the best method if it's possible, but I wonder; will the mixpre-d still send phantom power when in line-in mode? My 722 will (and I've done it a number of times for that same reason) but the usbpre2 won't since they are different connectors (but does have a -15db pad option on the input).



edit: no, it won't, it's an either/or setup. Now that I've looked at the specs, I can see what's the issue. The AKGs are like 30 mv/pa which means they are pushing past the minimum clip point of the box. While not recommended in many other mic systems, AKG has stated in the past that you can run the pads on the mics (which knocks it down to something like 7mv/pa or something like that) without sonic deficiency. I'd go that route unless you have some really HQ pads to run between the XLR cables and the mixpre-d.
« Last Edit: November 28, 2011, 02:47:06 PM by page »
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kirk97132

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Re: Limiters?
« Reply #3 on: November 28, 2011, 02:48:54 PM »
My experience with the SD preamps is that they have a hot output(MP-2 and USBPre2)  I run the pads on my Pre2 since at loud shows I was getting overs at lowest setting.  I do not run limiters on the preamps.  And if the 460's are like the 480's then you must be recording some pretty loud shows if you are getting such high levels.  I know the 480's are not the best choice in a very loud environment.  I cannot speak to the mixpre-D specifically.  But my MP-2 which is transformer based has been able to handle very hot inputs at very loud shows.  Granted I had to run it turned all the way down. 

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Re: Limiters?
« Reply #4 on: November 28, 2011, 04:04:15 PM »
My experience with the SD preamps is that they have a hot output(MP-2 and USBPre2)  I run the pads on my Pre2 since at loud shows I was getting overs at lowest setting.  I do not run limiters on the preamps.  And if the 460's are like the 480's then you must be recording some pretty loud shows if you are getting such high levels.  I know the 480's are not the best choice in a very loud environment.  I cannot speak to the mixpre-D specifically.  But my MP-2 which is transformer based has been able to handle very hot inputs at very loud shows.  Granted I had to run it turned all the way down.

that was my theory as well, but the manual says the max mic input before clipping is -10dbu and at approximately 125spl (1khz measurement blah blah blah) the AKGs are putting out close to +2dbu (based on the sengpiel chart which I've used with success in the past).
"This is a common practice we have on the bus; debating facts that we could easily find through printed material. It's like, how far is it today? I think it's four hours, and someone else comes in at 11 hours, and well, then we'll... just... talk about it..." - Jeb Puryear

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Offline eclark

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Re: Limiters?
« Reply #5 on: November 28, 2011, 04:26:56 PM »
The AKGs are like 30 mv/pa which means they are pushing past the minimum clip point of the box. While not recommended in many other mic systems, AKG has stated in the past that you can run the pads on the mics (which knocks it down to something like 7mv/pa or something like that) without sonic deficiency.

Just wondering where you got that information about the 30 mV/Pa (and 7 mV/Pa with the -10dB pad)?

From the material I have seen (AKG documentation) it says "C 460 B comb-ULS/61 Technical Data: Sensitivity at 1,000 Hz: 8 mV/Pa ; 0.8 mV/µb ; -62 dB ref. 1 µb."

However, based on the chart you linked to, even with 8 mV/Pa at 124spl/1kHz the maximum output of the mic will be -10dBu, which is the minimum mic input clipping level for the Mix Pre-D.
« Last Edit: November 28, 2011, 08:00:17 PM by eclark »
akg 460b + ck61 (-10db) > MixPre-D > Sony PCM M10

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Re: Limiters?
« Reply #6 on: November 28, 2011, 08:23:13 PM »
The AKGs are like 30 mv/pa which means they are pushing past the minimum clip point of the box. While not recommended in many other mic systems, AKG has stated in the past that you can run the pads on the mics (which knocks it down to something like 7mv/pa or something like that) without sonic deficiency.

Just wondering where you got that information about the 30 mV/Pa (and 7 mV/Pa with the -10dB pad)?

The padded volume was purely a guess based on the 480's reduction which falls to around 6 mv/pa when padded. I swore the 460s were in that similar region since they are similar.

From the material I have seen (AKG documentation) it says "C 460 B comb-ULS/61 Technical Data: Sensitivity at 1,000 Hz: 8 mV/Pa ; 0.8 mV/µb ; -62 dB ref. 1 µb."

I think those figures are based on the old sensitivity standard cause -62db even at comes out to something like 7.94 mv/pa when you use the 74db = 1ubar spec. If you knock 10db out of that you're left with ribbon sensitivity using today's standards which doesn't make sense, plus, we don't hear about people saying that their 480s need much less gain than the older 460s. I have no idea how to convert them to and from to get comparable numbers so I took a stab and used something in the ballpark of the 480s, sorry for the confusion.
"This is a common practice we have on the bus; debating facts that we could easily find through printed material. It's like, how far is it today? I think it's four hours, and someone else comes in at 11 hours, and well, then we'll... just... talk about it..." - Jeb Puryear

"Nostalgia ain't what it used to be." - Jim Williams

Offline eclark

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Re: Limiters?
« Reply #7 on: November 28, 2011, 10:05:47 PM »
I think I've figured out that with the -10dB pad, the C 460 B hits the -10dB minimum mic input clipping level exactly (at -10dB). So, theoretically, I think there is still possibility of clipping when running the pad, and a much higher chance without the pad. Note that this would only be if the sound in the room hit 134dB! But at 124dB, I think I've got some good headroom with the pad on.

I'll probably also set the limiter threshold to prevent the possibility of any input clipping because I like to run my levels hot.

So, I'm trying to decide what I want to do. I'd like to be able to use some more of the gain on the preamp, so I've considered getting a Denecke PS-2 to power the mics and then run line-in to the Mix Pre-D. I'll probably try it with the pad and see how manageable my levels are.

Also, I tested the Mix Pre-D and have confirmed that it does not output phantom power when on the "line" in setting. I'm using the 460s with selectable 12V on the MixPre-D.
« Last Edit: November 29, 2011, 08:42:12 AM by eclark »
akg 460b + ck61 (-10db) > MixPre-D > Sony PCM M10

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Re: Limiters?
« Reply #8 on: November 29, 2011, 10:42:03 AM »
I have run my 460s with the -10 switch for years since it is indeed a sensitivity control, not an attenuator pad in the traditional sense, and does not impact the mic's performance other than increase the max spl and decrease the output, both favorable effects for loud shows.

With the mics set at -10 my SD MP-1s run at 36db gain, which is just right. I always have the limiters on, but rarely see them engage. The limiters in SD preamps are optical, so there is no issue with having them on to protect against extreme transients.
AKG C460B w/CK61/CK63>Luminous Monarch XLRs>SD MP-1(x2)>Luminous Monarch XLRs>PMD661(Oade WMOD)

Beyer M201>Luminous Monarch XLRs>PMD561 (Oade CMOD)

Offline eclark

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Re: Limiters?
« Reply #9 on: November 29, 2011, 11:07:08 AM »
So, what is a good threshold for the limiters for a loud rock show? The Mix Pre-D does from +6dBu to +18dBu.

I've got the Sony PCM-M10 and I set the gain on that unit to -20dB (via the tone oscillator on the MixPre-D which supposedly outputs a -20dB signal). This tone oscillator registers on the Mix Pre-D at 0dB, and the Sony is "over" at 0dB. So I'm thinking even if the limiter is at +18dBu, I'll be safe with the M10 (because MixPre-D "0" is -20dB on the Sony). I'm going to try with the gain on the Sony to -12dB, which is between 7 and 8 on the M10's dial.

The setup will be AKG C460B (-10dB pad engaged) + CK61-ULS > 12V Phantom mic-in > Sd MixPre-D ideally at between 24dB and 36dB gain with limiters set +6dBu to +18dBu > Tape-out > Line-in of the Sony M10 at 24/48.

So, I guess I can use the -10dB pad on the mics to control the input clipping which is possible with the C460B/MixPre-D combo. And I'll set the gain on the M10 to -20dB -12dB and use the limiters on the MixPre-D to control the output clipping.
« Last Edit: November 29, 2011, 01:02:42 PM by eclark »
akg 460b + ck61 (-10db) > MixPre-D > Sony PCM M10

 

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