Hot audio without being in the red?

The MM1 does not have a tone ocs,. Like other SD products it works splendidly into a +4dB input.
It was designed primarily for boom ops, so advanced metering and tone was omitted. It does have a limit/peak LED.
 
NorBro said:
Is it possible for audio to be hot/distorted, but software shows levels to be only barely in the yellow here or there. There are no red peaks. We recorded some stuff and the levels in the camera showed the audio was around -12dB, but it appears to have been recorded lower and then some parts (the pops) are hot/distorted for a millisecond here or there, but the levels don't show red.

This is the first time this has happened to me. Any thoughts? Thank you.
Click to expand...

Why yes, it is very possible to clip a device in the chain and then under record it further on down the chain. You need to educate yourself on gain structuring. If I blast a mic preamp to 100%, yell into it, and then record into a recorder at -25, there's going to be a horribly distorted signal recorded quietly.

Imagine taking a polaroid of the sun, and then shaking it, laying the blown out polaroid on the ground and taking a well exposed shot with a DSLR. Would you wonder, "Why is the polaroid still blown out?!" hahaha

Here's a good article: http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html
 
Thanks guys. I actually did some more tests and it's definitely overloading the preamp. I used AC power with my preamp and tested two different Sennheiser shotgun microphones (MKH416 and MKE600) on two different cameras and even into a zoom recorder.

I can use 18, 28 and 36 (dB) on the preamp, but anything above starts distorting. I did a test at 66dB and you couldn't even understand what I was saying in the recording...but the levels bounced at -12dB.

So it's either a bad preamp or it's supposed to be like this. Anything below 36dB works perfectly.
 
"or it's supposed to be like this"
> I would surmise the gear is not broken.. just not hooked up correctly.
The output on the MM1 is 'Line level' (balanced nominal +4dB), therefore the following device's input *must* also be set to line level. If the camera has XLR inputs they can likely be switched to line level.
NOTE: Attenuation (ATT) settings in cameras normally only affect the mic level mode.. and this is NOT Line level. Repeat: The camera's audio input *must* be set to LINE. Read the camera's manual on how the switch to audio input to line level.
 
NorBro said:
Thanks guys. I actually did some more tests and it's definitely overloading the preamp. I used AC power with my preamp and tested two different Sennheiser shotgun microphones (MKH416 and MKE600) on two different cameras and even into a zoom recorder.

I can use 18, 28 and 36 (dB) on the preamp, but anything above starts distorting. I did a test at 66dB and you couldn't even understand what I was saying in the recording...but the levels bounced at -12dB.

So it's either a bad preamp or it's supposed to be like this. Anything below 36dB works perfectly.
Click to expand...
Sounds to me very much like the the higher gain settings of the preamp are overdriving the camera inputs, as others have suggested. The MM-1 is designed to drive a +4dBu input and has enough gain when cranked up to take a very low level dynamic mic's signal and boost it that far. The camera specs indicate the camera's line level sensitivity is 0dBu while the MM-1 has enough gain the easily exceed that with higher output mics. It's very unlikely the mic is overdriving the preamp. Instead, as has been mentioned before, one can clip right at the camera's inputs and distort the signal BEFORE the recording level control can tame it. Try this setup procedure ... connect mic to preamp to camera. Camera input to line level of course, preamp gain full down, preset and lock down camera recording gain to 2/3 scale. Gradually increase the preamp gain while speaking into the mic simulating a normal recording environment, increasing preamp gain until the camera meters refelct a normal recording level for speech, -12 dBFS or so. The preamp gain setting so determined becomes the standard setting for that mic, do not try to use the preamp gain to ride levels during recording. Instead, treat it as a coarse level control with fine tuning during the scene done with the recording levels on the camera. A more typical application for the MM-1 is as a headphone amp for the boom operator and a line-driver between the boom operator and a mixer where the mixer is riding gain - the MM-1 is set to a standard level for the mic in use and left there.

BTW, the rated output of the Senn MKH416 is about -30dBu @ 1Pa SPL. You said you discoverd exceeding the +36 setting on the preamp produced distortion. Well, adding 36dB gain to the -30dBu mic takes it up to +6dBu, well over the camera's nominal input rating. (Admittedly normal speech isn't as loud as 1Pa but you get the idea of the balancing act required to get the gain staging right.)
 
Last edited:
Too many variables involved. Typically, a test tone is sent to the following device (camera/recorder) from the preamp/mixer for calibration. The preamp is then 'adjusted' according to the acoustical level to achieve optimum record levels. This is basic audio-101. You should pick-up one of the frequently mentioned books by Ty Ford or Jay Rose.
 
NorBro said:
What would be a safe amount of preamp gain applied to a microphone like the Sennheiser MKE600?

http://www.bhphotovideo.com/c/product/878340-REG/Sennheiser_MKE_600_Shotgun.html
Click to expand...
Depends ... the optimal setting for the intimate conversation between two lovers will be quite different from recording flight operations on a carrier deck. You want to send the camera a signal that will have the meters at a proper level when the input gain is between a half and two-thirds the way up.
 
I don't have test tone and my setup is very basic. I'm going from the MM-1 preamp into a zoom h1 recorder. It's set to line. On the preamp, I have the choices of 18, 28 or 36 (any higher setting causes overload as others have mentioned). I have been keeping it at 18 or 28 to be safe and input levels in the zoom recorder are around 40-50 on a scale of 0-100.

The recordings sound great...but I was just wondering for my own knowledge.
 
I'm very confused now. As we suggested, the cause of the distortion is the preamp settings, and the camera is happily recording whatever is presented to it's input.

The preamp gain settings are selected to match the levels you supply the preamp with - so if you are somewhere really quiet, with a quiet sound source, you'll be using loads of gain (and probably accepting a little noise that's the consequence of low level and too much distance) while next day you could be searching for an extra pad when you're recording at the Formula 1 grand prix and can't hear yourself think, let alone monitor anything.

Seriously though - to make audio decisions, you need to listen. The various adjustable settings just help you get the best audio, but watching a meter, and prodding some buttons guarantees very little. Once you start to get to know the equipment better - the meters mean more, and your decisions get better. My recorder has 3 gain settings, and the level knob has a pretty wide range, so turned up on one gain setting gives very similar meter readings to turned down on another - BUT - I know that once I get above around 70% on the knob, the preamp is going to get a little noisy. However, I know that the source material may well completely hide it, or not - depending on what the sound is. So maybe having a lot of 'knob' control can be a real benefit for one recording, where levels are going to significantly change regularly, while another will change very little but any extra hiss is unwanted. I also know what happens to the sound if I mess up and push the levels. I've noticed that even not hitting 0 on the meter can sound a little rough - the waveform doesn't flat top, but just sounds less good. So I routinely record a little less hot, which with digits doesn't matter that much.

I often provide audio in theatre to video people, and I have a send that is +4dB, balanced on an XLR. I usually start with the fader about half way, and the signal peaks on my desk rarely hitting yellow from green, let alone red. Some camera people ask me to go up or down just a small amount, and they're happy. Others want me to turn down, and down, and down - and are clearly then using a mic type gain setting. It must sound awful by the time it's been mangled by this - but I guess they've not worked a system to get line down to mic - I'd use a DI if my camera didn't have a line level input, but me reducing my output to almost nothing is a rotten way of getting audio in, but they seem to do it.
 
NorBro said:
I don't have test tone and my setup is very basic. I'm going from the MM-1 preamp into a zoom h1 recorder. It's set to line. On the preamp, I have the choices of 18, 28 or 36 (any higher setting causes overload as others have mentioned). I have been keeping it at 18 or 28 to be safe and input levels in the zoom recorder are around 40-50 on a scale of 0-100.

The recordings sound great...but I was just wondering for my own knowledge.
Click to expand...
Glancing at the online manual for the H1 it appears the input gain setting shows on the display as a number between 0-100. Set it to 60. Adjust the preamp gain to give you a level on the meters of about -12dBFS with normal speech. The maximum input level for the recorder is 0dBm - if you set the preamp too high it's likely to exceed that and distort before the recorder's gain controls can have any effect.

How exactly are you getting the MM1's XLR output to connect to the recorder's 1/8 input? What cables/adapters are you using and exactly how are they wired?
 
Sorry for the confusion. Yes, I was using it with a camera before too. I've used this preamp with a Panasonic HPX250, Sony PMW200, 5DmkII, GH3, and a Blackmagic Pocket Cinema Camera. I've been using it with the pocket lately and I record straight into the H1 recorder. Sync audio later in post.

Regardless, EVERY single setup I had produced a large amount of distortion/modulation/broken audio when too much gain was applied from the Sound Devices MM-1 preamp. As Steve House mentioned, too much gain is overloading the preamp before the levels can even do anything. No matter if the levels for any of the cameras were almost completely down, there was too much gain overloading both of my microphones - Sennheiser MKH416 and MKE600. When the preamp was below 36dB, the audio sounded fine.

My setup:

Shotgun Mic IN to Sound Devices MM-1 MIC IN XLR input via http://www.bhphotovideo.com/c/product/996334-REG/kopul_m3006_bl_premium_cable_xlr_m_to.html

LINE OUT via XLR cable (same as above) OR XLR Female to 1/8 TRS Male cable via http://www.bhphotovideo.com/c/product/889779-REG/Sennheiser_KA_600_Connection_Cable.html

If using a camera with XLR inputs, the XLR cable from the OUT goes into the camera. Switch to Line. Turn phantom power off because I'm using phantom power from the MM-1. If I'm using the pocket, the 1/8 cable above goes straight into the LINE input of the H1 recorder and automatically switches the recorder into LINE mode. I then adjust the levels on the recorder.

Steve - when I want to be extra safe, I use 18dB gain from the preamp and my levels exactly fall in the 55-65 range on the H1 recorder to produce -12dBFS.

I know audio can be very complicated and there's so much to learn. As of now, for the very little audio work I do, I was just interested in learning if there was a number in every mic's specs that I can use and follow a formula on how much preamp to apply. So far, adding more than 36dB of gain from my preamp to 2 Sennheiser mics has caused major overloading. This makes me wonder what piece of equipment can possibly use upto the 66dB that the MM-1 offers!?
 
A dynamic mic has quite a bit lower output than does a condenser mic. Try using something like a Sennheiser MD46 or an ElectroVoice RE-50 reporter's mic and you'll find it needs the extra gain. Remember too that the MM-1 is designed to drive professional +4dBu line level inputs. Consumer gear line level is a nominal -10dBv, ~12 db lower than the pro line level (dBu and dBv have different voltages as their zero reference points so it's about 12 dB difference, not the 14 you'd expect). Zoom says the maximum line input level of the H1 is 0dBm and the MM-1 can easily exceed that.
 
Last edited:
I'm going to test one of the juicedLink or Beachtek preamps and see what the difference is compared to the MM-1.
 
NorBro said:
I'm going to test one of the juicedLink or Beachtek preamps and see what the difference is compared to the MM-1.
Click to expand...
Your problem is not the MM-1 itself, your mic is not overloading it. The problem originates at the input to the camera or recorder. There's a preamp there as well and the recording gain control comes after the input circuits. If you feed the recorder too hot a signal, the input preamp can overload before the gain control has any effect. Just keep the MM-1 at an appropriate gain setting and you'll be fine.

You can get an idea of the relative outputs of various mics by looking at the sensitivity rating - they give the output of the mic in either -dB or millivolts when it's exposed to a sound pressure of 1 Pascal, about 95 dBSPL. The actual output in real use depends on the volume of the sound being recorded so there's no way to come up with a standard number that says "with that mic use this gain" as it's situation dependent.
 
Last edited:
As Steve stated "the MM-1 is designed to drive professional +4dBu line level inputs".
Therefore it would be expected to overdrive a -10dB input occasionally. So a reduced output level from the MM1 is would be wanted, either by lowering the MM-1 input level, OR.. by inserting a pad between the MM1's output and H1's input. Using a 12 or 15dB pad should yield slightly better performance with all the components at their optimal performance settings.. the MM1's limiter would be better utilized and much less likely to overdrive the H1 input stage.
 
Really appreciate you guys contributing and trying to help me understand - thank you. Last question. When I have my preamp set on 0dB gain, what exactly is it doing? The audio still seems like it's much cleaner than if I plugged straight into the XLR inputs of my camera. When I plug straight into the camera, I hear so much background noise and room ambiance I guess you can call it. Is the preamp still making the audio clean even when set to 0dB?
 
Not sure of your set-up. 0dB gain on what pre amp. On the MM1, that's neither hear not there, gain adj. would depend on the source SPL, mic sensitively and other factors.
You may be hearing the camera's on board mic on the other channel. You should hear a difference between XLRs, but not night and day.
 
You must log in or register to reply here.
Back
Top