Q2 Audio F765 500 Series Operator's manual

F765 500 Series Compressor/Limiter
Operation Procedure: Quick Start
This is the ADR recommended set-up procedure to get the audio levels set up properly.
a . Set the COMPRESSOR 'RATIO' switch to 1:1 (non-operative and the PEAK LIMIT switch
to ‘ON’ (or 'PRE.EMPH' if your application will require de-essing and the channel OUTPUT
control turned down.
b . With the SYSTEM bypass switch to ‘OUT’ (i.e. by-passing the F765 vari-loss amp section
the audio levels to/from the F765 should be established in the usual way as though the F765
were not in the signal path. The audio level feeding the F765 should be peaking to at least
-10dBm, but preferably to 0dBm in order to obtain maximum compression possibilities.
c . Having established the normal level, switch the F765 SYSTEM bypass to ‘IN’ and adjust
the channel INPUT control until the overall amount of gain reduction likely to be required is
indicating on the meter (example: 8dB . At this stage the Peak Limit section is working and
red indicator will be flashing.
d . Turn up the channel OUTPUT attenuator and adjust so that the level is peaking to the
same level as the direct (dry signal. This is best done under dynamic signal conditions rather
than with a tone if monitoring with VU meters. A relevant direct comparison is now available
between direct and compressed signal at the flick of the SYSTEM ‘IN' / 'OUT’ switch at closely
approximating peak levels.
e . With the COMPRESSOR 'RATIO' control select the ratio required (e.g. 2:1 and adjust the
COMPRESSOR 'THRESHOLD' control until the red LIMIT LED only indicates on peaks above
the amount of compression required (move the threshold down from ‘0’ towards the -20 point
until the red LIMIT LED goes out, then come back one position. The PEAK LIMIT section will
then operate on any further unexpected increase in level. The amount of compression may be
changed by increasing/decreasing the channel INPUT control and adjusting the compressor
threshold to adjust the relationship between compression and peak limiting. Once set-up it will
not be necessary to alter the channel OUTPUT level (as per step ‘d’ . It is important to note
that the THRESHOLD control is based off of the output of the Vari-Loss Amp (preamp , not
the input level as in modern VCA type compressors.
f . The 'RELEASE' time in the compressor section will be adjusted for effect as well as the
'ATTACK' time.
g . In adjusting the compressor section always reference it to the PEAK LIMIT even if the
PEAK LIMIT is then switched out during operation. This maintains the optimum signal-to-

noise level in the system. When using the tighter slopes in the compressor the threshold will
lie just under the PEAK LIMIT in position -2 to -8 (3:1 to 20:1 ratios .
h . The compression slopes are calculated on a 15dB range of gain reduction. (i.e. the 2:1
ratio is established in the set-up procedure as 30:15 . It will be found in practice that the initial
ratio in that position is more akin to 1:1.5 becoming slightly tighter as gain reduction
increases. Thus, if only 6dB of compression were required this will be softer than the ratio
indicated and the next position higher could be selected. In practice this will not be of great
importance but it is useful to know of.
Compressor Side-Chain Access:
The F765 has a mix bus output as well as side chain access as specified by Radial
Engineering for their Workhouse™ racks. To allow 'Vocal Stressor' or 'ducking' type effects ,
the input to the compressor side-chain may be accessed via the 1/4” TRS Omniport™ jack on
the rear panel of the Workhorse™. A 1/4” TRS cable will need to be made or purchased with
your preferred terminations on the send and return, this could be XLR, TR/TRS, etc.,
depending on your connection needs. The side chain send must not see a lower impedance
than 10K ohms (minimum load of 10K ohms . To utilize the side chain access, there is a two
pin jumper on “CN4” that must be pulled to allow the return to operate (the send is always
active . It is located under the top cover at the rear of the F765. Store the jumper plug on one
pin of the 2-pin header so it will not be lost.
If you are not using the Omniport™ it is recommended to not have anything plugged into it
that could load or otherwise cause problems with the active send which is the Vari-Loss
amplifier output. The send and return are unbalanced.
The Omniport™ contacts are assigned as follows:
Tip=send
Ring=return
Sleeve=ground
Specifications (the need-to-know stuff :
Power: requires +/-16V DC at 70mA per rail.
Input impedance: 10K ohms unbalanced
Maximum output level: Balanced, 20dBu, 18.5dBm
Attack:
Peak Limiter: < 250uS for 100% control of overshoot – without any over limiting. (measured at
1KHz for 10dB gain reduction .
Compressor: 250uS, 2.5mS, 25mS.
Release:
Peak Limiter: 250mS
Compressor: 25mS, 50mS, 100mS, 200mS, 400mS, 800mS, 1.6 secs, 3.2 secs + Auto
release function.
Stereo Linking: The F765 must be ordered as a matched stereo pair to guarantee accurate
stereo linking. The peak limiter side chains are not linked, only the compression side-chains.
When linking for stereo, set BOTH channels the same (threshold, ratio, release, etc. so each
channel will contribute equally to compression.

Connector Pinout:
1 Chassis/Earth
2 Output +
3 N/C
4 Output -
5 Audio Ground
6 Stereo Link
7 “Omniport”™ Side Chain Return
8 Input -
9 “Omniport”™ Side Chain Send (min 10K loading
10 Input +
11 Bus output (per Radial Workhorse™ specs
12 +16V
13 0V (Audio Ground
14 -16V
15 N/C
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