Topic: Sound Devices MixPre-3 and 6, Part 3

[dallman]

ok. I recorded an acoustic set last night with my MixPre-6.  Ch 1-2 were the SBD.. my levels looked great all night, think I even turned them down slightly at one point..came home to almost seeing a flatline wavform..levels peaked at -49db.  I've used it before and this didn't happen...what gives? anyone know?  on the plus side..I brought the levels up to 0 in Soundforge and still sounds great, I hear no hiss at all.

Did you have the LR mix shut off? There is a known flaw that will drop your levels way down but everything will look normal. As far as I know (and from my own experience) this will only happen if you do not record the Mix. As you said, you can boost and there is no loss of quality at all. I am tempted to try really boosting while recording so I am in the red, in this L/R mix off mode to see what happens, but I also don't want to take a chance that I'll get a low but when boosted distorted signal.

[dogmusic]

ok. I recorded an acoustic set last night with my MixPre-6.  Ch 1-2 were the SBD.. my levels looked great all night, think I even turned them down slightly at one point..came home to almost seeing a flatline wavform..levels peaked at -49db.  I've used it before and this didn't happen...what gives? anyone know?  on the plus side..I brought the levels up to 0 in Soundforge and still sounds great, I hear no hiss at all.

Did you have the LR mix shut off? There is a known flaw that will drop your levels way down but everything will look normal. As far as I know (and from my own experience) this will only happen if you do not record the Mix. As you said, you can boost and there is no loss of quality at all. I am tempted to try really boosting while recording so I am in the red, in this L/R mix off mode to see what happens, but I also don't want to take a chance that I'll get a low but when boosted distorted signal.

From my experience, this level drop when not recording LR Mix only occurs in Custom Mode. If you stay in Advanced Mode -- and set your channel levels from the menu rather than from the fader knobs -- this is not a problem. You can turn off the LR Mix record and get normal level in your channels.

[mountaintaper]

ok. I recorded an acoustic set last night with my MixPre-6.  Ch 1-2 were the SBD.. my levels looked great all night, think I even turned them down slightly at one point..came home to almost seeing a flatline wavform..levels peaked at -49db.  I've used it before and this didn't happen...what gives? anyone know?  on the plus side..I brought the levels up to 0 in Soundforge and still sounds great, I hear no hiss at all.

Did you have the LR mix shut off? There is a known flaw that will drop your levels way down but everything will look normal. As far as I know (and from my own experience) this will only happen if you do not record the Mix. As you said, you can boost and there is no loss of quality at all. I am tempted to try really boosting while recording so I am in the red, in this L/R mix off mode to see what happens, but I also don't want to take a chance that I'll get a low but when boosted distorted signal.

Yes, i had the L/R record disabled.  well I guess I will record the useless mix in the future to avoid this.

[dallman]

ok. I recorded an acoustic set last night with my MixPre-6.  Ch 1-2 were the SBD.. my levels looked great all night, think I even turned them down slightly at one point..came home to almost seeing a flatline wavform..levels peaked at -49db.  I've used it before and this didn't happen...what gives? anyone know?  on the plus side..I brought the levels up to 0 in Soundforge and still sounds great, I hear no hiss at all.

Did you have the LR mix shut off? There is a known flaw that will drop your levels way down but everything will look normal. As far as I know (and from my own experience) this will only happen if you do not record the Mix. As you said, you can boost and there is no loss of quality at all. I am tempted to try really boosting while recording so I am in the red, in this L/R mix off mode to see what happens, but I also don't want to take a chance that I'll get a low but when boosted distorted signal.

From my experience, this level drop when not recording LR Mix only occurs in Custom Mode. If you stay in Advanced Mode -- and set your channel levels from the menu rather than from the fader knobs -- this is not a problem. You can turn off the LR Mix record and get normal level in your channels.

That's good to know. I like having the fader knobs control gain, but until the issue gets fixed, there really is no reason to not just set gain from the menu.

[jbell]

Hopefully a firmware update will be released soon to fix this issue. 

[F.O.Bean]

My second outing with the MP6:

https://archive.org/details/dco2017-06-22

I had AA batteries in for backup and it seemed to rely on those first as I got a low power warning in first set. My assumption is that I hadn't kicked on the USB battery pack first, so it defaulted to AA.

Yeah I bet that's what happened Alex! If you DO NOT hit the USB Battery button to turn it ON, it WILL NOT kick ON by itself! Ive had that happen on my old 70D's, so I look for the powering option immediately when starting my decks now!

And as far as the 5/6 1/8" inputs, I haven't tested mine yet! I'm going to hook my VMS02IB up to it and see what happens! I also have those Naiant MPD XLR Attenuators, that I can run between the VMS02IB & the MixPre6, if the +20db of fixed gain is too much for the MP6 to handle! I'd imagine if you had Channels 5/6 set to LINE IN, and had it really low at like -40db, I'd think it would be pretty hard to clip!

Thanks for all of the good info in these threads, yinz guys

[F.O.Bean]

ok. I recorded an acoustic set last night with my MixPre-6.  Ch 1-2 were the SBD.. my levels looked great all night, think I even turned them down slightly at one point..came home to almost seeing a flatline wavform..levels peaked at -49db.  I've used it before and this didn't happen...what gives? anyone know?  on the plus side..I brought the levels up to 0 in Soundforge and still sounds great, I hear no hiss at all.

Did you have the LR mix shut off? There is a known flaw that will drop your levels way down but everything will look normal. As far as I know (and from my own experience) this will only happen if you do not record the Mix. As you said, you can boost and there is no loss of quality at all. I am tempted to try really boosting while recording so I am in the red, in this L/R mix off mode to see what happens, but I also don't want to take a chance that I'll get a low but when boosted distorted signal.

From my experience, this level drop when not recording LR Mix only occurs in Custom Mode. If you stay in Advanced Mode -- and set your channel levels from the menu rather than from the fader knobs -- this is not a problem. You can turn off the LR Mix record and get normal level in your channels.

Hmmm, that's weird. Ive been recording the TV with realistic levels peaking around -8 to -12db, with 4 channels of 60v PFA's on Channels 1-4, with the LR Mix both ON & OFF, and I never had this issue! And fwiw, Ive been strictly using Custom Mode & adjusting the levels via the gain knobs ONLY Wonder why I haven't experienced that yet?

So for right now, it's just better to give my 4 channels of 60v PFA's on Channels 1-4, and set it through the menu with like +20db of gain via the menu?

I'm setting everything up AGAIN and testing to see if my Hosa Y Cable works [Dual XLR_F to Single 1/8"] for a SBD Patch and I need to determine which channel is Left & Right, since the Hosa cable isn't marked And I also need to test out the runtimes of my new Anker PowerCore+ 20,100 USB C Battery and see how long she goes

[willndmb]

^ For most mics and recording situations, the +10 dBu line input should be usable.  As an example, a Schoeps MK41 (14 mV/Pa) puts out +10 dBu at 139 dBSPL, which is insanely loud (Schoeps specs the max at 132 dB).  Even a few feet from the drums, it is unlikely to reach that level.  If you add gain, though, it's definitely possible.  I would think that a pre-amp with zero (or little) gain should almost always be OK, whereas something like an nbox (which I recall has 20 dB fixed gain) might cause problems.  I think in Noah's case, the issue was the 20 dB he added at the recorder.  I guess SD's specs could be off too (actually takes less than +10 dBu).

Soundboards are a different thing entirely, though...

ohh good to know and as typical I learn something new that I didn't know or misunderstood.
Thanks

[dogmusic]

I'm experiencing a strange problem with time of day on the MixPre-6. When I insert my 64 GB SD card with MixPre recorded files into my Mac computer, the time of the creation of the recorded file is shown as four hours earlier than the actual time it was recorded.

I have changed the Time Zone in the MixPre settings but it has no effect on the time shown on the file. It's always four hours earlier.

Adding to the puzzle is that my 32 GB SD cards do not exhibit this problem. They show the actual time of recording -- and it doesn't matter what the Time Zone setting is.

Anyone else noticed this?

EDIT: I have the latest firmware installed in the MixPre.

[MIQ]

^ For most mics and recording situations, the +10 dBu line input should be usable.  As an example, a Schoeps MK41 (14 mV/Pa) puts out +10 dBu at 139 dBSPL, which is insanely loud (Schoeps specs the max at 132 dB).  Even a few feet from the drums, it is unlikely to reach that level.  If you add gain, though, it's definitely possible.  I would think that a pre-amp with zero (or little) gain should almost always be OK, whereas something like an nbox (which I recall has 20 dB fixed gain) might cause problems.  I think in Noah's case, the issue was the 20 dB he added at the recorder.  I guess SD's specs could be off too (actually takes less than +10 dBu).

I'm thinking the same thing.  Shouldn't be a problem with most mics operating below their Max SPL ratings, with 0dB preamp/batt box gain.  I think DPA 4060s with a Batt Box into this input would be good to hear.  Here's a few Mic Outputs in dBu at their Max SPL:

     Mic                Sensitivity     Max SPL       Output @ Max SPL
________           ________     _______      ________________
DPA 4060            20 mV/Pa      134 dB               8.2 dBu
DPA 4061              6 mV/Pa      144 dB               7.7 dBu
Schoeps MK4       13 mV/Pa      132 dB               2.5 dBu
Schoeps MK41     14 mV/Pa      132 dB               3.1 dBu
MBHO KA200N     14 mV/Pa      130 dB               1.1 dBu
MBHO KA100DK   12 mV/Pa      132 dB               1.8 dBu
AKG CK61/62/63  20 mV/Pa      140 dB             14.2 dBu    with C480B

-MIQ

[tom the taper]

I'm experiencing a strange problem with time of day on the MixPre-6. When I insert my 64 GB SD card with MixPre recorded files into my Mac computer, the time of the creation of the recorded file is shown as four hours earlier than the actual time it was recorded.

I have changed the Time Zone in the MixPre settings but it has no effect on the time shown on the file. It's always four hours earlier.

Adding to the puzzle is that my 32 GB SD cards do not exhibit this problem. They show the actual time of recording -- and it doesn't matter what the Time Zone setting is.

Anyone else noticed this?

EDIT: I have the latest firmware installed in the MixPre.

YES!
Drivin me crazy.  The deck shows my current time, but regardless of what "GMT" setting, the .wav file shows 4 hours earlier.  (128 GB card)

~have to record the mix tracks, time is screwy, doesn't keep your last setting when you power up -- I'm READY for a Firmware Update!!

[tom the taper]

 
But I love my mix pre 6

[willndmb]

^ For most mics and recording situations, the +10 dBu line input should be usable.  As an example, a Schoeps MK41 (14 mV/Pa) puts out +10 dBu at 139 dBSPL, which is insanely loud (Schoeps specs the max at 132 dB).  Even a few feet from the drums, it is unlikely to reach that level.  If you add gain, though, it's definitely possible.  I would think that a pre-amp with zero (or little) gain should almost always be OK, whereas something like an nbox (which I recall has 20 dB fixed gain) might cause problems.  I think in Noah's case, the issue was the 20 dB he added at the recorder.  I guess SD's specs could be off too (actually takes less than +10 dBu).

I'm thinking the same thing.  Shouldn't be a problem with most mics operating below their Max SPL ratings, with 0dB preamp/batt box gain.  I think DPA 4060s with a Batt Box into this input would be good to hear.  Here's a few Mic Outputs in dBu at their Max SPL:

     Mic                Sensitivity     Max SPL       Output @ Max SPL
________           ________     _______      ________________
DPA 4060            20 mV/Pa      134 dB               8.2 dBu
DPA 4061              6 mV/Pa      144 dB               7.7 dBu
Schoeps MK4       13 mV/Pa      132 dB               2.5 dBu
Schoeps MK41     14 mV/Pa      132 dB               3.1 dBu
MBHO KA200N     14 mV/Pa      130 dB               1.1 dBu
MBHO KA100DK   12 mV/Pa      132 dB               1.8 dBu
AKG CK61/62/63  20 mV/Pa      140 dB             14.2 dBu    with C480B

-MIQ

so akg at max would be too hot, correct?
And if I was running akg ck_ into a tinybox on low gain (+4db), at max it def would be
But the typical loud show would be approximately sayyyyyyyy 126 and in turn be 0dBu (+4 with the tb) and not cause a problem

[johnw]

I have a hard time figuring this out because the gain reported in dB is not the same thing as dBu. So mk41 (3.1dBu @ 132dB) + Nbox (fixed 20dB gain) does not mean that the output is 23.1 dBu since you can't sum dB and dBu as they aren't the same units of measurement.

[MIQ]

Hi johnw,

You are right that it can be confusing.  In this case, since the preamp is applying a fixed amount of gain to the signal, it is ok to add the amount of gain it is adding in dB to the signal size in dBu to get the final signal size delivered to the recorder's 1/8" input in dBu. 

The confusing part is that gain is just multiplying the signal size (Volts) by a number like 10.  But when you express this in dB you ADD it (20 dB) to the signal size (also expressed in a dB scale: dBu).  You are right that you cannot mix dB scales that have different references like dBu and dBV.  In this case we are staying in the dBu scale from the input to the output.

The scenario you are describing is exactly the issue.  If you add (in dB) too much gain to the mic's signal, you will make the mic so sensitive, that even moderately loud sounds will overdrive the MixPre 1/8" input. 


Willndmb,

AKG at max SPL is too hot even if the preamp has gain=1 (0dB) but that doesn't mean you can't get a great recording since most shows are not going to be that loud at the mic location.   

Here's the dB-SPL that it takes to hit the +10dBu level for the AKG mics (or the DPA 4060, or any mic with sensitivity = 20 mV/Pa) and NO additional preamp gain.

Gain = 0 dB (Pre set to unity gain)
AKG SPL @ 10 dBu Output = 136 dB SPL

If you are adding gain (in dB) in the preamp, you will need to subtract the gain you are adding from the max SPL you can expose the mic to.  Adding gain makes the mics more sensitive so you can't expose them to as loud an environment.

Gain = +4dB (tb)
AKG SPL @ 10dBu Output = 136 dB SPL - 4 dB = 132 dB SPL. 
 
Gain = +20dB (Nbox)
AKG SPL @ 10dBu Output = 136 dB SPL - 20 dB = 116 dB SPL

The MixPre 1/8" input won't work in loud environments with many mics if you add too much gain between the mics and the 1/8" input.  But if you can keep the gain you are adding between the mics and the 1/8" input around unity, it should be ok for most mics.  I guess as more people try different combinations of mics, pres, and dB SPL into this input, we will see...

MIQ