SD-302, Setting the Output Limiter Threshold

[James Kuhn]

First, I know this subject has been discussed numerous times. The SD-302 manual, v.3.6, says the Output Limiter can be adjusted from +4 dBu to +20 dBu in 1 dB increments. I've read various threads and I've personally had numerous recommendations anywhere in the range of +10 dBu thru +18 dBu (SD factory default setting is +20 dBu...go figure?).

A friend and Sound Engineer whom I respect enormously, recommended I set the Output Limiter to +4 dBu and when I questioned him he said, "Look at the 'spec', above +4 dBu the Total Harmonic Distortion (THD) and Signal to Noise ramps-up significantly." Sure enough, I look in the 'specs' and it says, "THD + Noise, 0.007% typical (1 kHz, +4 dBu at Line out)" and "0.009 max (50 Hz to 20 kHz, +18 dBu, at Line out, fader fully up). I will say my 'friend' is an "audiophile" with ears like a Bat. Heh, heh! I don't know if this is considered 'significant' amoungst we mere mortals, but if the object is to have less 'distortion and noise', isn't increasing the 'Output Limiter Threshold', above +4 dBu, counter-productive? I'm trying to wrap my head around this concept.

I'm seeking enlightenment not controversy.

Thanks,

J.

[Rick Reineke]

It depends...on the following gear's input and level.
It most instances, a +4dB threshold is WAY to early. +4dBu is the nominal output level (voltage) and usually associated with a reference test tone, ie: OVU= -20dBFS or a +4dBu output voltage..actually 0dBu on the 302 and actual program audio can typically peaks much higher than the nominal level.. up to +20dBu on the 302 w/o clipping.
For a +4dBu (nominal) line level input recorder, I usually set the 302's limiter threshold @ +17dB which catches unexpected peaks and in turn the LED limit indicator flashes occasionally. Some folks are more conservative, others less, in overall levels and the limiter threshold setting.
Keep in mind, limiting in general produces distortion and excessive limiting will be quite audible and trash the sound.
PS: I believe the factory default limiter threshold setting on the 302 is +18dB.. or at least there abouts.

[James Kuhn]

Rick...thank you for your thoughtful response. My 'Rig' is a "Dual-System", SD-302 Mixer, to an HXR-NX5U and a Marantz PMD-661 using the "Tape-Out/Mix-Out", which has a nominal level of -15 dBu. I'm trying to find the elusive 'sweet spot' and more importantly, I like to know I'm doing certain things.

Regards,

J.

[Gary Nattrass]

Hi Rick what are you referencing +18db to???

That sounds way to high to me and with line up levels in the UK for broadcast .775v 1khz tone set at:

-18dbfs
0db PPM
-4dbvu

and a maximum level of:
-10dbfs
+8db PPM
+4dbvu

I don't understand where you get +18db from, do you mean set the limiter at +18 above -20dbfs but that would only leave you 2db of headroom in the digital domain for US scaling and nothing in the UK reference where 0dbfs is equal to +18db PPM.

Personally I set all my limiters to come in at +6db with reference to PPM scaling so that corresponds to the following:

-12dbfs
+6db PPM
+2dbvu

Note from the original question you will never in a million years hear the difference between THD of .007% and .009% and that tolerance or probably more down to the test set and will vary with components so is a nominal measurement. It is also better to under modulate digital devices as the noise is better than trying to get the max level recorded as we had to in analogue days if you peak to -12 to -10 dbfs it will still give you a further margin of headroom even if you are not using limiters at all.

[Steve House]

A limiter setting of +18dBu where +4dBu = 0VU = -20dBFS means the limiter will kick in if the mixer tries to drive the recording device above -6dBFS. Leaving it at the factory default of +20dBu still leaves a 4dB safety margin before hitting 0dBFS.

[James Kuhn]

Gary - "...you will never in a million years hear the difference between THD of .007% and .009%..." I agree, but have you ever met a true 'audiophile'? Heh, heh! No disrespect to any 'audiophiles' out there.

Gentlemen, I truly appreciate this discussion and the information contained within. It's why I love this Forum!

Best regards,

J.

[Gary Nattrass]

James it all depends if you have oxygen free brain cells or not! ;0)

some times for most TV work just getting a signal recorded can be the main challenge!

[Trevor Dennis]

I did that wet finger on a crystal wine glass last night while my wife and I were watching TV, but I couldn't make it work. Then my wife put her hands over her ears and the cat ran off! Now my wife is ten years younger than me, and I have worked in some noisy environments, but it was very disconcerting to discover how limited my high frequency hearing has become. I can just about hear the 8KHz tone in the following link (I am 63).

What is your hearing range? | egopont

[Steve House]

Interesting site. At 67 my ears are easily good through 16kHz and from there up through 18kHz it's on the edge of perception. 19 and 20 are a definite no-go.

[Rick Reineke]

Originally Posted by Gary Nattrass

Hi Rick what are you referencing +18db to???

In my case, +17dBu is the output limiter's threshold. My 302's calibration tone is normally set to 0VU, (not to be confused with 0 dBFS - OR - 0dBu) the following recorder's level meter gets set to -20dBFS... via the XLR out..
If I need a mic level output from the XLR for instance, I adjust the Output level via the software menu which only affects the XLR,.