Frequently Asked Questions - Focusrite OctoPre Instructions Manual

FREQUENTLY ASKED QUESTIONS

Is the OctoPre a Class A device, and why is that
important?
Yes, the OctoPre is a Class A device. Why? Well, Class A is a type of amplifier design
in which you have a standing DC current running through your amplifier circuits all
the time. As the signal comes along you vary what you're taking from that, rather than
switching between supplying a positive current for one half of the waveform and a
negative current for the other half. This results in the ability to represent audio in a
linear (distortion free) manner all the way through the circuit. Cheaper processors use
IC amplifiers which run close to Class B and don't have the same standing DC current,
which means the transistors inside the chips switching off and on, inevitably resulting
in less linear performance.
My OctoPre gets quite hot when in use. Should I be
worried about this?
No. This is a result of the high-quality Class A circuitry inside your OctoPre and
should not be a problem. As a precaution, it is wise to rack hotter units lower down
your rack than cooler units. If space is available, fit a blank panel between units to
allow extra ventilation.
Should I use balanced connectors with my OctoPre?
Yes, the line level analogue inputs and outputs are balanced, operating at +4 dBu. See
the 'Rear panel connections' section on page 2 for more information on connecting
the analogue line level inputs and outputs. However, if using an unbalanced
instrument source, you should connect to the unbalanced 1/4" inputs on channels 1
and 2.
Does the OctoPre have the same kind of spectacular
bandwidth that has given the Red and ISA range units
their reputation for 'open-ended' sound?
Yes. The audio bandwidth of the OctoPre is 10 Hz to 200 kHz!
Can I take my OctoPre with me when I travel
internationally?
It depends. There are two versions of the OctoPre mains transformer. One is suitable
for use in North America and Japan, with mains voltages in the 100-120V range. The
other version is designed for use in the UK and Europe, with mains voltages in the
200-240V range. If you buy an OctoPre in a particular territory, it will be configured
for ONLY that territory's mains voltage range. For example, if you're travelling from
the USA to the UK, you CANNOT use your US model OctoPre. But if the mains
voltage in the country you're visiting is in the same range, you can use the OctoPre
with no problems – so taking an OctoPre from the USA to Japan, or from Germany to
France, for example, would be fine.
Is there an optional digital input card?
No, because all the processing in the OctoPre is entirely analogue - so even if there
were a digital input, the digital signal would have to be immediately pass through a
D/A converter to allow processing!
Why is the 24 bit 96kHz specification important?
An A/D converter works by sampling the audio waveform at regular points in time,
and then quantising those values into a binary number, which relates to the number of
bits specified. The quantised signal must then be passed through a D/A converter
before it becomes audible. In simple terms, the D/A essentially 'joins the dots' plotted
by the A/D converter when the signal was first converted to digital. The number of
dots to join, combined with how little those dots have been moved, determines how
accurate the final signal will be compared to the original. The greater the sample rate
and bit rate, the more accurate the whole digital process is. So 24 bit/96 kHz
performance will ensure more accurate digital transfer of your audio information
compared to the old 16 bit/44.1kHz standards. This is especially important if further
digital signal processing is to be applied to the signal once converted to digital, as any
mathematical operations taking place on the data (for example as a result of a gain
change, or dynamic effect process) may result in quantisation and rounding errors. The
higher the resolution of the digital data, the smaller the audible effect of these errors.
Can I retrofit a digital board to an analogue OctoPre at
a later date?
Yes, and you can do it yourself - it can easily be retro-fitted by the customer without
any soldering etc, just a few screws to undo, and one clip-connector to join to the
main PCB.
How are the multiple digital outputs configured?
At 48kHz or lower: the 8 AES or SPDIF (switch-selected from rear panel) outputs
can run simultaneously with 8 ADAT™ outputs, plus 8 ADAT™ outputs from the
second port (hence 24 simultaneous outputs in total). The ADAT™ outputs are exact
duplicates of each other. All output formats put out the same set of 8 channels in terms
of sample rate, dither etc.
At 96kHz: same as above, except that the two ADAT™ ports carry output channels
1-4 and 5-6 respectively (hence 16 simultaneous outputs in total).
In simple terms, the A/D puts out three separately buffered sets of 8 channels at
48kHz, or two separately buffered sets of 8 channels at 96kHz.
ENGLISH
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