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Offline noam

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702 limiter
« on: January 06, 2017, 01:39:07 PM »
Anyone has extensive experience with recording with the 702 (or 7xx series) with the limiter on at high gain? I had bad experience with the limiter on with the SONY PCM D1, and I wonder if the limiter can cause problems like holes in the sound at sudden loud sounds, etc. Is there a scenario of using it (for acoustic music) and ruining the recording? What happens to loud clapping with the limiter on? On the PCM D1 every loud clap punched a hole in the sound.

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Re: 702 limiter
« Reply #1 on: January 06, 2017, 04:42:08 PM »
Other than knowing that Sound Device's limiters are implemented in the analog input stage rather than after the ADC (a good thing which makes them more transparent) and that they are less problematic than many other implementations, I'm not intimately familiar with the behavior of the limiters in their recorders. 

However, the basic principle remains constant-

Some limiters are implemented in a more transparent way than others, yet all of them squash signal dynamics once the signal crosses the threshold.. which is their intended job.  Limiting while recording is a last-ditch safety measure and should be regarded as such.  I'm not suggesting that limiters on a recorder should not be employed. I am suggesting that if the limiter actually has to do what it is designed to do, that indicates a failure of the recordist to set recording levels appropriately.  If you get away with it without bad sonic repercussions, consider yourself fortunate and set your levels lower the next time.

Yes, some recordings benefit from a reduction of dynamic range.  But trying to do that via bumping up against the "safety limiter" at the recorder's input is not an optimal way of doing that, and I'll dare call relying on that method to do so, lazy.

Record with low enough levels so that you have sufficient headroom to encode all expected auditory events (including applause of course, if expected!), then readjust the signal level afterwards as appropriate.  Unless your levels are so low that the electronic noise-floor of your equipment begins to exceed the ambient acoustic noise-floor of the environment in which the recording was made, there is no drawback to doing so.  If using quality equipment at the level of SD gear, there will be more than enough dynamic range available into which the entire musical signal will fit- from the quietest hiss of the empty room to the loudest impulse of the performance peak or audience applause eruption.   If the finished recording would benefit from a reduction in dynamic range, do that afterwards in such a way that you have control over it and can limit (pun) the negative consequences.

Consider it similar to tracking and fading while making the recording.  It's much easier to do, and do well, afterwards.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

"Narrow or widely spaced microphone configurations are preferred. It is well-known experience that pure coincidence microphone concepts are not able to produce a satisfying natural spatial impression, due to the lack of adequate interchannel temporal relations (time-of-arrival, phase, correlation)" -Günther Theile
"The mix of the Double M/S signals with a large A/B configuration of omnis results in the spacious sound that is often desired. This option also provides decorrelated low-frequency signals." -Helmut Wittek

Offline boltman

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Re: 702 limiter
« Reply #2 on: January 07, 2017, 02:00:15 AM »
It's worth pointing out that the SD recorders, like their peers, are designed mostly for film dialogue.  Most production sound mixers use limiters.  If the gain structure is set up properly, and the limiter is used as a safety as intended, it is pretty transparent.

Offline noam

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Re: 702 limiter
« Reply #3 on: January 09, 2017, 12:54:54 PM »
, it is pretty transparent.

What does it mean transparent?

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Re: 702 limiter
« Reply #4 on: January 09, 2017, 02:11:13 PM »
^ isn't audibly obvious as it squashes the dynamics.  A trained ear may still be able to identify it working, but casual listeners will not.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

"Narrow or widely spaced microphone configurations are preferred. It is well-known experience that pure coincidence microphone concepts are not able to produce a satisfying natural spatial impression, due to the lack of adequate interchannel temporal relations (time-of-arrival, phase, correlation)" -Günther Theile
"The mix of the Double M/S signals with a large A/B configuration of omnis results in the spacious sound that is often desired. This option also provides decorrelated low-frequency signals." -Helmut Wittek

Offline boltman

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Re: 702 limiter
« Reply #5 on: January 09, 2017, 06:24:36 PM »
As Gutbucket noted above, music tapers rarely use limiters, basically because there is no reason to.  You can find a reasonable recording level that will not introduce hiss by being too low, nor be brickwalled by being too high. 

Film people almost always use limiters, but many would argue that they do not need as high a resolution as music recorders.  On-set or on-location dialogue is usually competing with other sounds that make the ultrafi recording requirements of, let's say an orchestra, quite different.  You may, or may want to, mic your acoustic music source closely, in which case the clapping really won't be an issue. 

Offline voltronic

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Re: 702 limiter
« Reply #6 on: January 09, 2017, 09:05:05 PM »
Lots of great advice above.  I'm solidly in the camp of avoiding limiter use for music recording entirely, even if I had access to good analog limiters (which I currently do not).

I'm also an acoustic / classical recording person, and I find that limiters (even good ones) can be audible with music that has wide dynamic swings.  Unless the limiter is very "soft" or you never hit the threshold, you can often hear it working and I find the sound distracting.

In cases where I cannot do a true sound check (more often than not) I much prefer to record a set of duplicate "safety" tracks at a lower level, though I set the main tracks conservatively so it's rare I need to use the safeties.

As far as applause, I won't use my omnis if there is audience nearby the mic stand and/or I have to place farther away from the ensemble.  I set my levels low enough so that the applause does not clip, then I reduce it in post using one of the methods linked below, and finally raise the level of the entire concert.

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Offline dream

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Re: 702 limiter
« Reply #7 on: January 12, 2017, 01:30:01 AM »
I have a 744T and I really like the limiters. They are very good with fast transients which would do overshots, like during recording fireworks. Of course limiters are off where levels are predictable, especially in music recording.

Offline noam

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Re: 702 limiter
« Reply #8 on: February 26, 2017, 07:56:11 AM »
Last night at a staged opera performance I did what I wanted to try a long time - test the limiter on the 702. I ran a very hot signal with the limiter on. The results are impressive. The limiter is indeed very transparent. It is way better than digital compression - you don't hear any of the signs of compression you get with digital compression. This is the most valuable circuit in the 702 - the pre-amps have been matched by now by cheaper units. For my purposes, to bring the singers' voices on stage behind the orchestra pit up front, this limiter is pure gold.

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Re: 702 limiter
« Reply #9 on: February 26, 2017, 08:09:31 AM »
Last night at a staged opera performance I did what I wanted to try a long time - test the limiter on the 702. I ran a very hot signal with the limiter on. The results are impressive. The limiter is indeed very transparent. It is way better than digital compression - you don't hear any of the signs of compression you get with digital compression. This is the most valuable circuit in the 702 - the pre-amps have been matched by now by cheaper units. For my purposes, to bring the singers' voices on stage behind the orchestra pit up front, this limiter is pure gold.

Why is it preferable to do this at the recording stage? You could always alter the dynamic range of your files in post and aren't limited to the attack, release, and ratio settings of the fixed SD limiter.
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Offline noam

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Re: 702 limiter
« Reply #10 on: February 26, 2017, 09:03:35 AM »
Last night at a staged opera performance I did what I wanted to try a long time - test the limiter on the 702. I ran a very hot signal with the limiter on. The results are impressive. The limiter is indeed very transparent. It is way better than digital compression - you don't hear any of the signs of compression you get with digital compression. This is the most valuable circuit in the 702 - the pre-amps have been matched by now by cheaper units. For my purposes, to bring the singers' voices on stage behind the orchestra pit up front, this limiter is pure gold.

Why is it preferable to do this at the recording stage? You could always alter the dynamic range of your files in post and aren't limited to the attack, release, and ratio settings of the fixed SD limiter.

Because it sounds much better. It's day and night. Maybe my digital software is not the best, maybe I don't know how to use it best. I have many problems with digital compression that don't come up with the 702 analog limiter. The digital compression gives an artificial sound with more listening fatigue. I have a hard time deciding whether to choose the trigger signal for compression at minus infinity, which raises the noise floor, or at 3 dB - 5 dB above the noise floor, which creates pumping. Also, no matter what I do digital compression gives me clipping and I have to reduce the volume of the entire file by at least 5 dB. It just sucks.

Offline noam

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Re: 702 limiter
« Reply #11 on: February 26, 2017, 09:23:52 AM »
There is something strange about the 702 limiter. I've been taping at that venue for 22 years, 8 with the 702, and I know how the wav form should look like at a given gain level. Last night I used the mic sensitivity set at "normal" instead of "low" for the first time ever. When I tested the signal, a whisper sent the LED  metering ballistics to red, so I set the gain knob at 12 o'clock, which was still very hot. When I tested the result during intermission, the signal was too low, so I turned the gain knob up to 4 o'clock. I already knew from testing at home that the live LED metering ballistics give me an exaggerated false reading - maybe they give a reading without the limiter, the actual recorded signal is always lower with the limiter, but I was not prepared for what I found out when I opened the files at home with SoundForge editing software. The files from before intermission with the gain set at 12 o'clock  had the wav form look exactly like it would with mic gain sensitivity set at "low", it was almost flat earth, not "normal" like it did, only the applause, which always is the loudest signal stood like skyscrapers kissing zeros, instead of hills like it would with the sensitivity set at "low". This indicates to me that the limiter aggressively reduced the entire signal way too much and only very loud signal showed the mic gain sensitivity was set at "normal".  The files from after intermission, with the gain knob set at 4 o'clock finally looks healthy, with loud choral passages at -6 dB, which is exactly like I want it, and the singers whispering on stage still giving me some little visible hill, not flat earth, which is perfect. The applause kissed zeros, but no ugly holes in the sound (is this what's called "overshots"?). Next time I will run the mic inputs again at "normal", but will turn the gain knob all the way up, with the limiter on.

The gear I used: Schoeps mk4 cardioids>Schoeps VST 62 IUg mic amp>Sound Devices 702
« Last Edit: February 26, 2017, 09:26:42 AM by noam »

Online Gutbucket

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Re: 702 limiter
« Reply #12 on: February 27, 2017, 09:08:22 AM »
There is a lot to be said for good quality tools well tailored to a task, which do not require extensive setting to sound good. The key here is that the 702 limiter is well implemented and it's parameters have been set appropriately by the Sound Devices engineers.  That's why it performs appropriately without too much negative sonic artifact.

But there is nothing magical about it.  The same or superior results can be achieved later, but one can only do so by using the equivalent quality limiter and setting it appropriately.  Learning how to set the parameters appropriately is the challenge.  The parameters interact in ways which may not be intuitively obvious.  Digital limiting has far greater capabilities and can be considerably more advanced than analog-implemented limiting, partly because since the file has already been recorded, a digital limiter can "see into the future" and otherwise analyze the signal in ways a real-time analog implementation cannot.  Whether or not use of such capabilities are appropriate is a different question.  Those additional parameters and options bring not only a potential for tuning the limiter more appropriately to suit the program material, but also a very real potential for not tuning things appropriately. 
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

"Narrow or widely spaced microphone configurations are preferred. It is well-known experience that pure coincidence microphone concepts are not able to produce a satisfying natural spatial impression, due to the lack of adequate interchannel temporal relations (time-of-arrival, phase, correlation)" -Günther Theile
"The mix of the Double M/S signals with a large A/B configuration of omnis results in the spacious sound that is often desired. This option also provides decorrelated low-frequency signals." -Helmut Wittek

 

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