Setting up DVX100 with Sound Devices 302 field mixer using full level signal.
(or how to match the clipping levels and find life easy ever after)
First some basic technical facts.
Pro audio gear use standardized line level voltages. This makes it easy to connect different units together, ideally they are perfectly mathced "out ot the box" so to speak. To check the match there is a 1 kHz test tone set at 0 dBVU reference level. The reason for the procedure described below is the fact that DVX100 is not a pro device and to make a perfect match with the Sound Devices 302 mixer the avarage utput level from the mixer needs to be lowered a bit. This is done once using the setup menu of the SD302. Later on when recording all level settings are done with the Gain and Fader knobs of the SD302 in the normal manner.
The audio scales used by the DVX100 and SD302 are different for historical reasons. DVX100 is a digital device, where 0 dB (zero desiBel) level means the absolute maximum sound level. Trying to record signals louder than 0 dB results in bad distortion as all the 16 sampling digits are used up at that point and trying to push it causes the waveform turn into a square wave. The last, fifth red marker on the DVX100’s audio meter is the 0 dBFS (desiBel Full Scale) level. Just touching it means all digits are used up and bad distortion is imminent, especially if the last red stays lighted for any amount of time. There are no +dB values in digital domain and can not be. The last white and red segments on DVX100 are at 2 dB increments, last white is -12 dBFS.
SD302 is an analog device and for historical reasons they use dBVU (desiBel Volume Unit) scales. On the SD302 the 0 dBVU level is a theoretical optimum saturation level for analog tape recorders. With those recorders it was (is) possible to overdrive the recorder without ill effects, the only thing that would happen would be some automatic limiting (dynamic range compression) and slight distortion. For that reason the optimum scale from 0 to +12 dBVU is marked orange and only the last 8 dB to +20 or clipping level, red.
What we need to do is to match the SD302 output to DVX100 input. The signal level out from SD302 must be optimized to line level in for DVX100, not to be too quiet (DVX100 preamp must amplify it too much causing noise), not too loud (this could cause clipping in DVX100 preamp). The aim is to set the audio dials on DVX100 to 12 o’clock position and leave them there. This is done with the full scale signal from SD302 by adjusting the signal out –level to match DVX100 inputs. The factory standard setting is too “hot”, meaning that it is possible to overdrive the DVX100 preamplifier even when the SD302-DVX100 combination is otherwise used correctly. We need to lower the output level to match DVX100 inputs.
- set DVX100 input switches to line (from front of camera), phantoms off, channel 1 to 1, 2 to 2 (under LCD)
- turn ALC off (DVX100 menu)
- turn audio dials pointing straight up, 12 o’clock position
- attach SD302 to DVX100, both channels driven
- enter the SD302 menu by tuning it on while pressing "PK/VU" button
- menu position 30 is entered, turn on the test signal with the switch MIC/1K (disconnect headphones first if any, loud signal!)
- the audio level bars on the DVX100 should light up all the way to last red, now lower the signal strength with the SD302 "Meter Brightness" button. The LED on the left channel row goes down, make it go down until the last red on the DVX100 turns off. This happens at -8 or -10 dBVU. If for some reason the level on SD302 was too low to begin with, turn it up with the "BATT" button.
- adjust the DVX100 audio dials just slightly so that the last red (almost) lights.
That’s it. Press "PK/VU" button enough times to exit menu and restart SD302. You will notice an orange LED glowing on the output side signifying that the output level is non-standard.
Now turn on the test tone again in the normal power-on mode. This gives a standard 0 dBVU level which is 20 dB lower than the full scale signal. You will find that this 0 dBVU signal strength sent to DVX100 shows the seventh white, five segments before first red. This is the -20 dBFS point on DVX100.
Next we set the output limiter on the SD302. I have it at +17 dBVU which gives a whooping 20*3=60 dB headroom for unexpected loud signals (the limiter has 20:1 ratio). That is plenty enough for every occasion and the limiter does not kick in too early to mess with good signals.
This is done by entering the menu mode again, see above, then pressing PK/VU once. Left channel -26 LED blinks. With "Meter Brightness" button and "BATT" button adjust the limiter threshold so that right channel +16 LED lights and +20 LED blinks. Now limiter threshold is at +17 dBVU. Exit menu by pressing "PK/VU"enough times.
Testing: attach your choice of microphone to SD302 and adjust levels on the SD302 with Gain and Fader knobs so that normal dialog lights up the orange LEDs on the SD302 (you must not touch the audio dials on the DVX100 anymore!). You will notice that when speaking louder you hit the first reds on the SD302 and DVX100 about the same time. Limiter lights start to light up on SD302 when there are 3-4 reds on the DVX100 scales. If you try to yell to the mic it is next to impossible to get the last red on DVX100 to light up*. We have arrived! All level setting is now done with SD302 and as long as you do not set the levels too high on SD302 there is no way the sound could get screwed on the DVX100, that is: as long as the average levels are around the orange range and loudest bits at first few reds on the SD302.
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*) this also means that in controlled situations slightly higher level from the SD302 could be used safely.
-------
This post was modified and expanded Feb 26:th 07 after reading the comments below. For that reason some of those corrections are outdated. Thanks all, all suggestions to make this as easy and exact as possible are welcome!
(or how to match the clipping levels and find life easy ever after)
First some basic technical facts.
Pro audio gear use standardized line level voltages. This makes it easy to connect different units together, ideally they are perfectly mathced "out ot the box" so to speak. To check the match there is a 1 kHz test tone set at 0 dBVU reference level. The reason for the procedure described below is the fact that DVX100 is not a pro device and to make a perfect match with the Sound Devices 302 mixer the avarage utput level from the mixer needs to be lowered a bit. This is done once using the setup menu of the SD302. Later on when recording all level settings are done with the Gain and Fader knobs of the SD302 in the normal manner.
The audio scales used by the DVX100 and SD302 are different for historical reasons. DVX100 is a digital device, where 0 dB (zero desiBel) level means the absolute maximum sound level. Trying to record signals louder than 0 dB results in bad distortion as all the 16 sampling digits are used up at that point and trying to push it causes the waveform turn into a square wave. The last, fifth red marker on the DVX100’s audio meter is the 0 dBFS (desiBel Full Scale) level. Just touching it means all digits are used up and bad distortion is imminent, especially if the last red stays lighted for any amount of time. There are no +dB values in digital domain and can not be. The last white and red segments on DVX100 are at 2 dB increments, last white is -12 dBFS.
SD302 is an analog device and for historical reasons they use dBVU (desiBel Volume Unit) scales. On the SD302 the 0 dBVU level is a theoretical optimum saturation level for analog tape recorders. With those recorders it was (is) possible to overdrive the recorder without ill effects, the only thing that would happen would be some automatic limiting (dynamic range compression) and slight distortion. For that reason the optimum scale from 0 to +12 dBVU is marked orange and only the last 8 dB to +20 or clipping level, red.
What we need to do is to match the SD302 output to DVX100 input. The signal level out from SD302 must be optimized to line level in for DVX100, not to be too quiet (DVX100 preamp must amplify it too much causing noise), not too loud (this could cause clipping in DVX100 preamp). The aim is to set the audio dials on DVX100 to 12 o’clock position and leave them there. This is done with the full scale signal from SD302 by adjusting the signal out –level to match DVX100 inputs. The factory standard setting is too “hot”, meaning that it is possible to overdrive the DVX100 preamplifier even when the SD302-DVX100 combination is otherwise used correctly. We need to lower the output level to match DVX100 inputs.
- set DVX100 input switches to line (from front of camera), phantoms off, channel 1 to 1, 2 to 2 (under LCD)
- turn ALC off (DVX100 menu)
- turn audio dials pointing straight up, 12 o’clock position
- attach SD302 to DVX100, both channels driven
- enter the SD302 menu by tuning it on while pressing "PK/VU" button
- menu position 30 is entered, turn on the test signal with the switch MIC/1K (disconnect headphones first if any, loud signal!)
- the audio level bars on the DVX100 should light up all the way to last red, now lower the signal strength with the SD302 "Meter Brightness" button. The LED on the left channel row goes down, make it go down until the last red on the DVX100 turns off. This happens at -8 or -10 dBVU. If for some reason the level on SD302 was too low to begin with, turn it up with the "BATT" button.
- adjust the DVX100 audio dials just slightly so that the last red (almost) lights.
That’s it. Press "PK/VU" button enough times to exit menu and restart SD302. You will notice an orange LED glowing on the output side signifying that the output level is non-standard.
Now turn on the test tone again in the normal power-on mode. This gives a standard 0 dBVU level which is 20 dB lower than the full scale signal. You will find that this 0 dBVU signal strength sent to DVX100 shows the seventh white, five segments before first red. This is the -20 dBFS point on DVX100.
Next we set the output limiter on the SD302. I have it at +17 dBVU which gives a whooping 20*3=60 dB headroom for unexpected loud signals (the limiter has 20:1 ratio). That is plenty enough for every occasion and the limiter does not kick in too early to mess with good signals.
This is done by entering the menu mode again, see above, then pressing PK/VU once. Left channel -26 LED blinks. With "Meter Brightness" button and "BATT" button adjust the limiter threshold so that right channel +16 LED lights and +20 LED blinks. Now limiter threshold is at +17 dBVU. Exit menu by pressing "PK/VU"enough times.
Testing: attach your choice of microphone to SD302 and adjust levels on the SD302 with Gain and Fader knobs so that normal dialog lights up the orange LEDs on the SD302 (you must not touch the audio dials on the DVX100 anymore!). You will notice that when speaking louder you hit the first reds on the SD302 and DVX100 about the same time. Limiter lights start to light up on SD302 when there are 3-4 reds on the DVX100 scales. If you try to yell to the mic it is next to impossible to get the last red on DVX100 to light up*. We have arrived! All level setting is now done with SD302 and as long as you do not set the levels too high on SD302 there is no way the sound could get screwed on the DVX100, that is: as long as the average levels are around the orange range and loudest bits at first few reds on the SD302.
-------
*) this also means that in controlled situations slightly higher level from the SD302 could be used safely.
-------
This post was modified and expanded Feb 26:th 07 after reading the comments below. For that reason some of those corrections are outdated. Thanks all, all suggestions to make this as easy and exact as possible are welcome!
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