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Hello all,
Here's some measurements of the Focusrite OctoPre MkII 8-channel microphone preamp and ADAT ADC.
My unit is from 2011, so I guess you could say it's a vintage piece of gear
.
This unit can operate as a standalone analogue preamp (instrument/mic/line input direct to line output - without being digitized), or as an ADAT ADC - supporting sample rates up to 96kHz and an optional external clock source. It doesn't have a DAC at all.
Test equipment and setup
The measurements you're about to see were performed using:
Topping E50 DAC was used as the signal generator, and it was connected to the RME Babyface optical output (in S/PDIF mode); i.e. all three devices were synced to the same clock source via optical connections.
Maximum input levels
Maximum input levels with pad disengaged and with minimum gain position:
For sure this ADC won't top the SINAD chart, but THD+N is better than 16 bits (~17 bit), so that's IMHO pretty good. All channels perform similarly (as we'll see below).
Raising input gain by +15dB (half-way knob position) decreases SNR by ~5dB compared to minimum gain:
Increasing gain all the way (+50dB) decreases SNR by ~35dB compared to minimum gain:
TRS line input gave equivalent results for +15 dB gain position (note: I couldn't generate a large enough signal level to measure line input at minimum gain position at -1dBFS):
Instrument input exhibits about +17 to +20 dB worse THD compared to microphone and line inputs - but that is still quite OK for intended purpose:
Dynamic Range and Noise
Noise performance is pretty solid, noise floor is 106dB down (~17 bits). As we can see next, noise floor is pretty consistent in all channels:
Frequency Response
The frequency response is very flat in the 20Hz to 20kHz range which is the most important characteristic.
There appears to be a 0,2 dB channel imbalance between pairs of channels, but from previous measurements I know that my E50 DAC contributes 0,1dB of that. In any case IMHO inconsequential.
Measuring the frequency response from XLR input to line output (i.e. analogue preamp mode) using 192kHz sample rate shows no digitization and a very flat response in the audible range (note the zoomed-in vertical scale). Pure analogue signal path is also confirmed by measuring latency/delay compared to audio interface analogue loopback in REW - latency was measured to be 0,0000 ms indicating no AD/DA conversion.
Distortion
As we can see, all 8 channels pass the 16-bit threshold for distortion - which is IMHO pretty good for this kind of device!
Minimum THD+N is reached at 1,7Vrms / -1dBFS (peak) input. Minimum THD is at about -10 dBFS (peak) input.
Again Instrument input shows much worse distortion vs frequency behaviour (especially the rising 2nd harmonic with frequency):
Multitone
IMHO that is surprisingly clean!
Crosstalk
One performance metric where the OctoPre MKII doesn't perform very well is crosstalk - there's rising low-frequency crosstalk between specific pairs of channels: the "main" channel pairs (i.e. 1+2, 3+4, 5+6 and 7+8) show worse crosstalk performance compared to any other combination of channels (e.g. 1-3 or 2-3 or 1-8 are much better).
Here's an example - Ch1 vs Ch2 crosstalk is white, and Ch2 vs Ch3 crosstalk is green:
I've contacted Focusrite technical support about this and they confirmed this is expected behaviour. They also stated newer generations of the device (i.e. Scarlett and Clarett OctoPres) have significantly improved channel crosstalk.
Conclusion
All in all I'd say this is pretty good performance for a relatively inexpensive 8-channel microphone preamp / ADC combo device with quite a few features.
Realistically, the only slight let-down is the crosstalk performance - but even that is not really that big of a deal, considering the acoustic crosstalk you get in multi-mic recording sessions.
The device absolutely served me well enough through the years for the occasional band recording session, and still works perfectly!
Here's some measurements of the Focusrite OctoPre MkII 8-channel microphone preamp and ADAT ADC.
My unit is from 2011, so I guess you could say it's a vintage piece of gear
.This unit can operate as a standalone analogue preamp (instrument/mic/line input direct to line output - without being digitized), or as an ADAT ADC - supporting sample rates up to 96kHz and an optional external clock source. It doesn't have a DAC at all.
Test equipment and setup
The measurements you're about to see were performed using:
- RME Babyface Silver Edition audio interface (measurements)
- Topping E50 DAC (measurements)
- Room EQ Wizard (REW) software (for most measurements)
- RightMark Audio Analyzer (RMAA) software (for the crosstalk measurement only)
- Various cables and adapters
Topping E50 DAC was used as the signal generator, and it was connected to the RME Babyface optical output (in S/PDIF mode); i.e. all three devices were synced to the same clock source via optical connections.
Maximum input levels
Maximum input levels with pad disengaged and with minimum gain position:
- XLR/mic input: 1,9 Vrms / +7,8 dBu
- TRS line input: 25,7 Vrms / +30,4 dBu
- TRS instrument input: 1,8 Vrms / +7,3 dBu
- Input pad: -8dB
- Half-gain position: +15 dB
- Maximum gain position: +50 dB
For sure this ADC won't top the SINAD chart, but THD+N is better than 16 bits (~17 bit), so that's IMHO pretty good. All channels perform similarly (as we'll see below).
Raising input gain by +15dB (half-way knob position) decreases SNR by ~5dB compared to minimum gain:
Increasing gain all the way (+50dB) decreases SNR by ~35dB compared to minimum gain:
TRS line input gave equivalent results for +15 dB gain position (note: I couldn't generate a large enough signal level to measure line input at minimum gain position at -1dBFS):
Instrument input exhibits about +17 to +20 dB worse THD compared to microphone and line inputs - but that is still quite OK for intended purpose:
Dynamic Range and Noise
Noise performance is pretty solid, noise floor is 106dB down (~17 bits). As we can see next, noise floor is pretty consistent in all channels:
Frequency Response
The frequency response is very flat in the 20Hz to 20kHz range which is the most important characteristic.
There appears to be a 0,2 dB channel imbalance between pairs of channels, but from previous measurements I know that my E50 DAC contributes 0,1dB of that. In any case IMHO inconsequential.
Measuring the frequency response from XLR input to line output (i.e. analogue preamp mode) using 192kHz sample rate shows no digitization and a very flat response in the audible range (note the zoomed-in vertical scale). Pure analogue signal path is also confirmed by measuring latency/delay compared to audio interface analogue loopback in REW - latency was measured to be 0,0000 ms indicating no AD/DA conversion.
Distortion
As we can see, all 8 channels pass the 16-bit threshold for distortion - which is IMHO pretty good for this kind of device!
Minimum THD+N is reached at 1,7Vrms / -1dBFS (peak) input. Minimum THD is at about -10 dBFS (peak) input.
Again Instrument input shows much worse distortion vs frequency behaviour (especially the rising 2nd harmonic with frequency):
Multitone
IMHO that is surprisingly clean!
Crosstalk
One performance metric where the OctoPre MKII doesn't perform very well is crosstalk - there's rising low-frequency crosstalk between specific pairs of channels: the "main" channel pairs (i.e. 1+2, 3+4, 5+6 and 7+8) show worse crosstalk performance compared to any other combination of channels (e.g. 1-3 or 2-3 or 1-8 are much better).
Here's an example - Ch1 vs Ch2 crosstalk is white, and Ch2 vs Ch3 crosstalk is green:
I've contacted Focusrite technical support about this and they confirmed this is expected behaviour. They also stated newer generations of the device (i.e. Scarlett and Clarett OctoPres) have significantly improved channel crosstalk.
Conclusion
All in all I'd say this is pretty good performance for a relatively inexpensive 8-channel microphone preamp / ADC combo device with quite a few features.
Realistically, the only slight let-down is the crosstalk performance - but even that is not really that big of a deal, considering the acoustic crosstalk you get in multi-mic recording sessions.
The device absolutely served me well enough through the years for the occasional band recording session, and still works perfectly!
