I use both Audirvana and Audio Hijack to host Dirac Live Processor on macOS. While Audirvana offers a bit-perfect exclusive mode that shuts all sound but music, Audio Hijack enables system-level correction that also works for video content. I never thought these two hosts were any different until I saw the measurements.
To make things clear, let me explain the naming convention for my measurements. Take the first graph for example.
AudirThrough means when Audirvana is off or passing through the signal, and Dirac is also off. This shows the same effect as when Audirvana is turned off.
AudirDiracFull means Audirvana is on, Dirac is on and doing the full-range correction.
AudirDirac1kHz means Audirvana is on, Dirac is on and doing correction on the frequency response up to 1kHz. (From what I know Dirac is still doing phase correction above 1kHz and that cannot be adjusted.)
AudirDiracSwitch means Audirvana is on, and I am turning Dirac on and off, or I am switching between Dirac’s stored filters.
AudirDiracOff means when Audirvana is on, Dirac filter is off, but Dirac’s gain setting is still active.
Replacing Audir with Hijack and we got five more terms for what is happening when Audio Hijack is hosting Dirac.
8341+8341Filters means what it literally means. Later you will see the Genelec 8341 using filters designed for the Neumann KH80 and vice versa.
Off to the measurements. I use MMM and white noise.
First off we have 8341+8341Filters on Audirvana. As you can see in both the Log view and Linear view, I got some baffling results.
1. Audirvana on its own does not produce any anomalies in the high-frequency response.
2. When Dirac is on, the high-frequency response shows a zigzag. That is definitely not in the target response that I loaded. Where does that come from?
3. When Dirac is limited to 1kHz, the zigzag above 10kHz is still there. Shouldn’t the high-frequency response look like the AudirThrough response when no correction is turned applied?
4. A steep high-pass filter within the audible band? Really?
5. What is this notch? Pre-ring?
I thought Audirvana might be at fault, so I switched to Audio Hijack and found out that the hosting software actually affects the frequency response.
6. Still perfect.
7. Instead of zigzagging, the high-frequency response shows a slight roll-off, which, again, is not intended in my target response.
8. Again, limiting to 1kHz still affects all the way to 20kHz.
9. Same thing but more rolled off.
10. Same thing but more rolled off.
Then I thought perhaps the highborn Genelec was allergic to Dirac’s humble algorithm, so I switched up the speakers and the filters. I loaded an old set of Dirac filters designed for the KH80 and measured Audirvana’s response.
Well, on the 8341, when using Audirvana, the old KH80Filter behaved the same way as the newly designed 8341Filters.
Using Audio Hijack though, for some reason the notch disappeared. I rerun the remeasurements a few times and could not reproduce the notch here. But other problems are still there.
Finally, I measured the KH80 loaded with the set of Dirac filters designed for the 8341. The unintended roll-off and notch are back.
As for why these anomalies happened, I was hoping the technical experts on this site can give me some insight. By the way, before anyone suggests, I also have SoundSource. It behaved the same way as Audio Hijack did. Also in case anyone wants to see the smoothed response, here is one for the first graph.
To make things clear, let me explain the naming convention for my measurements. Take the first graph for example.
AudirThrough means when Audirvana is off or passing through the signal, and Dirac is also off. This shows the same effect as when Audirvana is turned off.
AudirDiracFull means Audirvana is on, Dirac is on and doing the full-range correction.
AudirDirac1kHz means Audirvana is on, Dirac is on and doing correction on the frequency response up to 1kHz. (From what I know Dirac is still doing phase correction above 1kHz and that cannot be adjusted.)
AudirDiracSwitch means Audirvana is on, and I am turning Dirac on and off, or I am switching between Dirac’s stored filters.
AudirDiracOff means when Audirvana is on, Dirac filter is off, but Dirac’s gain setting is still active.
Replacing Audir with Hijack and we got five more terms for what is happening when Audio Hijack is hosting Dirac.
8341+8341Filters means what it literally means. Later you will see the Genelec 8341 using filters designed for the Neumann KH80 and vice versa.
Off to the measurements. I use MMM and white noise.
First off we have 8341+8341Filters on Audirvana. As you can see in both the Log view and Linear view, I got some baffling results.
1. Audirvana on its own does not produce any anomalies in the high-frequency response.
2. When Dirac is on, the high-frequency response shows a zigzag. That is definitely not in the target response that I loaded. Where does that come from?
3. When Dirac is limited to 1kHz, the zigzag above 10kHz is still there. Shouldn’t the high-frequency response look like the AudirThrough response when no correction is turned applied?
4. A steep high-pass filter within the audible band? Really?
5. What is this notch? Pre-ring?
I thought Audirvana might be at fault, so I switched to Audio Hijack and found out that the hosting software actually affects the frequency response.
6. Still perfect.
7. Instead of zigzagging, the high-frequency response shows a slight roll-off, which, again, is not intended in my target response.
8. Again, limiting to 1kHz still affects all the way to 20kHz.
9. Same thing but more rolled off.
10. Same thing but more rolled off.
Then I thought perhaps the highborn Genelec was allergic to Dirac’s humble algorithm, so I switched up the speakers and the filters. I loaded an old set of Dirac filters designed for the KH80 and measured Audirvana’s response.
Well, on the 8341, when using Audirvana, the old KH80Filter behaved the same way as the newly designed 8341Filters.
Using Audio Hijack though, for some reason the notch disappeared. I rerun the remeasurements a few times and could not reproduce the notch here. But other problems are still there.
Finally, I measured the KH80 loaded with the set of Dirac filters designed for the 8341. The unintended roll-off and notch are back.
As for why these anomalies happened, I was hoping the technical experts on this site can give me some insight. By the way, before anyone suggests, I also have SoundSource. It behaved the same way as Audio Hijack did. Also in case anyone wants to see the smoothed response, here is one for the first graph.
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