All eight of the analogue inputs use “Combo XLR” connectors. These can accept male XLR connectors, TS (unbalanced) ¼” jacks or TRS (balanced) ¼” jacks.
When an XLR connector is used, the pre-amp automatically configures gain and impedance to receive microphone level signals. If a ¼” connector is used, the pre-amp is set to accept balanced or unbalanced line level signals. When INST mode is selected (on Channels 1 or 2), the ¼” input reconfigures again to optimise for an unbalanced, high impedance signal.
The two 48V switches apply 48 V phantom power to Mic inputs 1 to 4 and 5 to 8 respectively. Phantom power is required by most condenser (capacitor) microphones. Phantom power is only applied to the XLR contacts of the Combo connectors: thus if a group of 4 inputs is being used for both mic and line (or instrument) level signals, phantom power is only applied to the microphones.
Dynamic microphones do not require phantom power, but most will operate normally with phantom power supplied. Passive ribbon microphones do not require phantom power and may be damaged if supplied with phantom power.
If you are unsure about a microphone DO NOT apply phantom power without checking the manufacturer’s specifications first.
The gain of each channel should be adjusted to suit the incoming level; louder sources will need less gain than quieter ones. Always use the LED meters to check the signal level on each channel.
Start with the Gain control set to minimum. Play (or sing) at the loudest level that is likely to be reached during the song, and gradually increase the gain until the meter shows orange (-3 dB). Then lower the gain by a few dB. This should ensure that the signal level is unlikely to ever reach red (0 dB) and overload the A-to-D converter, which would result in distortion.
Note that the high headroom pre-amplifier design used in the Scarlett range means that a switchable Pad is unnecessary. (See Scarlett OctoPre Dynamic performance specifications for input sensitivity specifications.)
The red O/L LED should never illuminate; if it does, the gain is set too high.
Turning a channel’s COMPRESS control clockwise from its OFF position activates the channel’s compressor. As the control is moved from the OFF position, the yellow COMP LED will light briefly to confirm that the compressor is now active. As it is rotated clockwise, the compression threshold is progressively reduced, resulting in increasingly heavy compression. The yellow COMP LED will illuminate when compression is being applied to the signal, which will be the case whenever the signal level exceeds the threshold.
Pressing the MORE button increases the compression ratio, thereby applying more compression to the signal for the same setting of COMPRESS.
On the OctoPre, the COMPRESS control is essentially a combined Threshold and Gain Make-up control: as the threshold is reduced, causing more of the signal to be compressed, the compressor’s overall gain (often referred to as “Make-up Gain”) is increased, raising the signal level at the output to match that at the input.
In both modes the attack time is 1.2 ms and the release time is 28 ms.
The two graphs below show the compression characteristics in “Normal” and “More” modes respectively. The curves include the effect of the make-up gain on the overall signal level.
By connecting the line outputs of the OctoPre to the analogue line inputs of a mixing console (or any other device), the unit can be used either as a purely analogue, 8-channel microphone pre-amplifier, or as an analogue “break-out box” for ADAT signals when in ADAT > LINE mode.
The line outputs are balanced: for a balanced connection, use ¼” 3-pole (TRS) jacks, or ¼” 2-pole (TS) jacks for an unbalanced connection.
The maximum output signal level is +16 dBu (balanced), or +10 dBu (unbalanced).
Use the ADAT OUT optical port(s) [16] to connect the OctoPre to the ADAT input(s) of an audio device using TOSLINK optical cable(s).
The right-hand port (as viewed from the rear of the unit) can transmit eight channels of audio at 44.1 kHz or 48 kHz sample rate via a single optical cable.
At 88.2 kHz or 96 kHz sample rates, each port can transmit four channels of audio. The right-hand port carries Channels 1 to 4, the left-hand port carries Channels 5 to 8; thus two TOSLINK cables are required to transmit all eight channels.
At 176.4 kHz or 192 kHz sample rates, each port can transmit two channels of audio. The right-hand port carries Channels 1 and 2, the left-hand port carries Channels 3 and 4. The OctoPre is restricted to four channels of digital audio at these sample rates; the outputs of Channels 5 to 8 are not available via the ADAT ports.
Use the SAMPLE RATE switch [9] to select the desired sample rate frequency. It is essential that the sample rate selected on the OctoPre matches the sample rate set on the receiving digital device.
Use the OPTICAL IN ADAT port(s) if you need to convert digital audio (e.g., the output of a DAW) to analogue, using the Scarlett OctoPre Dynamic’s ADAT > LINE mode.
The right-hand port can receive eight channels of audio at 44.1 kHz or 48 kHz sample rate via a single optical cable.
At 88.2 kHz or 96 kHz sample rates, each port can receive four channels of audio. The right-hand port carries Channels 1 to 4, the left-hand port carries Channels 5 to 8; you need two TOSLINK cables to receive all eight channels.
At 176.4 kHz or 192 kHz sample rates, each port can receive two channels of audio. The right-hand port carries Channels 1 and 2, the left-hand port carries Channels 3 and 4. The OctoPre is restricted to four channels of digital audio at these sample rates.
Use the SAMPLE RATE switch to select the desired frequency. It is essential the sample rate selected on the Scarlett OctoPre Dynamic matches the sample rate set on the transmitting digital device.
A number of synchronisation options are available:
Connect the OctoPre to the receiving digital device via the ADAT OUT port(s) and ensure that the receiving device is set to source its clock from its ADAT input, and that the sample rates on both devices match.
On the OctoPre, set the SYNC to INTERNAL and the LED will light.
An alternative method to the above is to sync the receiving device to the OctoPre’s WORD CLOCK OUT using a BNC cable. In this scenario, set the receiving device’s sync source to its external word clock input.
Connect the OctoPre’s ADAT OUT port(s) to the receiving digital device’s ADAT input. Connect the digital device’s ADAT output to one of the OctoPre’s ADAT IN ports.
On the OctoPre, set the SYNC to ADAT and the LED will light. Also ensure both devices use the same sample rate.
Selecting ADAT > LINE mode ([12] on the front panel) reassigns the eight sources for the analogue LINE OUTPUTS [18]. In normal operation, the outputs of the mic pre-amplifier channels are available at these connectors; in ADAT > LINE mode, the connectors are fed with the ADAT digital signals at the ADAT IN port(s), following D-to-A conversion.
This mode enables the OctoPre to be used to connect an 8-channel ADAT format output (from a DAW, for example) to a set of analogue inputs, typically the channels of an analogue mixing console, to permit such a mixer to be used to mix down DAW tracks.
When ADAT > LINE mode is enabled, the eight microphone pre-amplifiers are still operational, and their outputs remain available at the ADAT OUT ports.