sound quality with field mixer

[Philip Fass]

I was reading some owners' opinions of the Sound Devices 302 mixer, in which they claim that even one mic plugged into the mixer instead of directly into the camera will produce better sound.

I can't figure out the logic of this. I can see how a bad electronic device could introduce noise or distortion, but how can a mixer actually improve the audio quality of a single track?

[Garrett Low]

Because you would be using the Mic Preamps in the SD mixer which are far superior to those in the camera. Then from the mixer you would take a line level in which would produce a signal with less noise.

-Garrett

[Philip Fass]

Thanks, Garrett.

If you compared clips recorded each way, what difference would you hear -- ie, what kind of noise is reduced with the mixer?

[David Dixon]

You might find this thread I posted over on dvxuser.com of interest. It seems that a mixer doesn't always really improve audio quality in every case. It adds some things that are beneficial, but if you have a pretty decent recorder (camera or not) the main help is in control, not quality.

The thread also includes a short test I did with/without a Sound Devices MixPre between the mic and the camera.

Opinions on this test?

[Jon Fairhurst]

The signal level out of a microphone is tiny. Add a fixed amount of noise (say from cheap preamps in a camera) to that signal and the ratio of signal to noise is small. On the other hand, if you use a great preamp that has a tiny amount of fixed level noise, the signal to noise ratio is much greater.

Now, amplify that high S/N signal with the good preamp and plug that signal into the cheap camera preamp. The camera input signal is now at a much higher level, but the fixed level of noise from the camera is the same as in the first example above. The end result is a much higher signal to noise ratio than you would get without the high quality preamp.

The key points are that the preamp must have a low noise level, and it must also have signal gain.

There are limits to this solution though. Drive the camera with too hot a signal and it will overload and distort. Like Baby Bear's porridge, the signal shouldn't be too hot or too cold.

[Greg Miller]

Originally Posted by Jon Fairhurst

if you use a great preamp that has a tiny amount of fixed level noise, the signal to noise ratio is much smaller.

Don't you mean "much greater"?

[Jon Fairhurst]

Yes, greater. I've edited and corrected the original post. Thanks!

[Philip Fass]

Given equally good technique, would it be right to conclude that an excellent mic plugged into a camera is better than a mediocre mic plugged into an excellent mixer?

[David Dixon]

OK, I'm pretty new at all this, so someone slap me down if I'm off base here, but...I think in general, yes.

If you don't have a decent mic, nothing else further down the chain can do much about it.

A good Sound Devices-level mixer won't make a mediocre mic sound great. Now, if you have a good mic but a mediocre recorder with noisy preamps, the mixer should make a more noticeable difference. The cleaner, quieter sound from the mixer would probably help keep the mediocre recorder from degrading the audio as much.

Here's a test I did:

Untitled on Vimeo

In this test I found adding the SD MixPre between the mic (AT 4053b) and camera (Canon XF100, xlr input, 16bit linear PCM) did not substantially improve the audio I was already getting. It's better, but not by much. It's just a touch fuller and smoother, and recording into a laptop @ 24 bit (also in the test) gave a very small further boost. So, I was already getting decent audio and the MixPre did not add very much.

The mixer can get you cleaner sound, better limiters, more control, etc., but it doesn't add audio quality that wasn't there in the first place.

[Gary Nattrass]

Well here is my take on it there is far too much hype and nonsense about kit for video, otherwise we would be all using oxygen free copper cables and mega bucks mics all the time.

Tv and film sound is not like hifi or recording studio stuff where you spend loads of cash to get that nirvana sound of mics taped on the walls of a room, nonsense.

Great sound for vision can be had by simply plugging a mic into your camera and making sure that you take care and attention to record the cleanest and best audio possible, just buying a mixer and plonking it in the chain will not get instant results its all about how you use your kit and understand it.

That extends to the full audio chain and you are good to know what the process of sound editing and dubbing is beyond what you record on location.

Even thought i have over 30 years in mainstream audio production for TV and film I now use budget kit most of the time and get great results that have been on broadcast productions around the world.

I use sony prosumer stereo mics with mini disc for wild recordings and AT875R and G2 radio mics as my stock kit direct into my HPX301 and 371 cameras, I have just bought a budget TW mixer to add more channels and edit in FCP and dub on a 10 year old digidesign 002 console running pro tools V8.

it's how you use what you have that matters and understanding what you may require in addition to make your location sound the best you can capture, I use auto level all the time on my P2 cameras as it is excellent these days and make sure that my audio gain structure from location all the way thru to delivery is spot on and does not introduce any nasty distortion or unwanted noise along the way.

Yes an expensive pre amp or mixer may improve things but the only way to tell is if I do an A/B comparison so I make sure that the kit I use it set up well and I understand it's limitations so that I get the best out of what I have rather than thinking that I need XY or Z to get better.

[Jon Fairhurst]

Originally Posted by Philip Fass

Given equally good technique, would it be right to conclude that an excellent mic plugged into a camera is better than a mediocre mic plugged into an excellent mixer?

A great mic plugged directly into a bad preamp will be noisy no matter what. Maybe you can clean some of the noise from the signal and bury the rest under music and sound design, but that's no fun. It can compromise artistic choice, and you still might end up with a noisy result with dialog that sounds somewhat underwater. The subtleties of the nice mic will be lost under the noise.

A mediocre mic in a good preamp will sound quiet, but the voices might sound dull and/or thin. With good EQ, this can be improved to some degree, but is unlikely to sound great. At least it won't be buried in noise.

In general, I'd lean towards a clean preamp and mediocre (but not bad) mic. A general audience won't complain about dull sounding voices, but they will notice noise and NR artifacts.

On the other hand, the great mic might have a stronger signal than the mediocre one, so that will help mitigate the noise to some degree. Still, the superior preamp probably wins the battle. Not all great mics have high sensitivity, and not all mediocre mics have poor sensitivity.

[Kirk Candlish]

Originally Posted by Gary Nattrass

I use sony prosumer stereo mics with mini disc for wild recordings and AT875R and G2 radio mics as my stock kit direct into my HPX301 and 371 cameras, I have just bought a budget TW mixer to add more channels and edit in FCP and dub on a 10 year old digidesign 002 console running pro tools V8.

Consumer mics today are better than many of the pro mics from a decade ago. That's a product of technology trickle-down and mass production in China. So that's no revelation.

Now if you're using the A/D converters of an 002 and getting away with it, well then I'd say you've compromised your sound. The 002 was cheap and accessible because of it, but it's converters were terrible.

I use a digi rack, but I'm using Benchmark A/D converters so I bypass the digi and it's merely a patchbay at that point.

But more to the point of the thread, a good mixer in experienced hands is going to give you control over dynamics that you simply can't get any other way. Through riding the gain and limiters the resulting signal to noise will be far superior to recording straight to the camera.

[Tom Morrow]

The one reason that hasn't been mentioned much is levels... a good shotgun microphone might not produce strong enough levels to maximize your dynamic range; my me66 which is known as being relatively hot still sometimes doesn't produce -12dbFS peak levels recording a person speaking relatively quietly from a bit of a distance, and that's with my Sound Devices MixPre. Running it into a camera or recorder directly and the levels are even lower (and therefore noisier).

I'm considering upgrading from the SD mixpre to the 302 partially for this reason, to get a bit more gain.

[Philip Fass]

Jon, is there a way to determine the quality of a camera's preamp without having a mixer to compare it to?

[Gary Nattrass]

Originally Posted by Kirk Candlish

Consumer mics today are better than many of the pro mics from a decade ago. That's a product of technology trickle-down and mass production in China. So that's no revelation.

Now if you're using the A/D converters of an 002 and getting away with it, well then I'd say you've compromised your sound. The 002 was cheap and accessible because of it, but it's converters were terrible.

I use a digi rack, but I'm using Benchmark A/D converters so I bypass the digi and it's merely a patchbay at that point.

But more to the point of the thread, a good mixer in experienced hands is going to give you control over dynamics that you simply can't get any other way. Through riding the gain and limiters the resulting signal to noise will be far superior to recording straight to the camera.

I totally take your point and the kit use inc the 002 is not the best on the market, but it is about getting the job done to budget these days and I have never had anyone comment that the production audio I do is not good enough for broadcast. I don't use the mic amps in the 002 anyway and as all my work is P2 tapeless all the audio stays in the digital domain for delivery so I make sure that my front end audio is squeaky clean, the pre amps on my panasonic cameras are very good and as said the auto gain circuits are very useable and help keep things in spec on location.

TV in the UK is all about compromise these days and before I had the 002 I used AMS Neve DFC and logic 3 consoles that cost up to £500k for my audio dubbing needs.

As for dynamics that is not really relevant for TV production sound as most of it is crushed in the dub to make it sound punchy and match the commercials that are compressed to oblivion. OK film sound may be different but most features dialogue is also compressed and mixed with limited bandwidth anyway.

My daily rates are the same or less than they were ten years ago so that is reflected in the kit I now buy and use, as technology has moved on you don't always have to get the most expensive to get acceptable results.