- The Profiler Model referred to in this thread is ...
- ☑️ Profiler Head/Rack
Dear Kemper users,
Hello, my name is Alexx Bean, and I am a recording artist (links below) using the Kemper Profiler Rack.
I prefer to record my Kemper via coaxial S/PDIF RCA cables into my Universal Audio Apollo x6, because such method reduces the number of A/D D/A conversions from three to one juxtaposed with recording the "Master Stereo" signal from the "Main Output."
With a recent OS update, many of us can turn our Kempers into USB audio interfaces. I was considering switching from S/PDIF to USB, so I decided to conduct a detailed test to compare the two methods. I measured the amount of time in samples from the "DI Analog" signal to the "DI High/DI" signal arriving from S/PDIF and USB respectively. For context, "DI Analog" is a straight analog split from input to "Direct Output." "DI High/DI" is a line level digital signal with correct phase lock with the amp sound. The result is that S/PDIF always comes out as having less time difference in samples from its "DI High/DI" signal to the "DI Analog" signal over the difference in time between USB's "DI High/DI" signal and the "DI Analog" signal. Please see test details below. I'm not saying USB does or does not sound better than S/PDIF, but S/PDIF certainly is "faster" than USB when configured properly and may give you better "feel" when tracking. S/PDIF is also "faster" than "Main Output" when configured properly (Kemper is Master Clock, 44.1kHz sample rate).
Couple of notes:
- If you connect your two S/PDIF cables from Kemper to Apollo, set your sample rate to 44.1kHz in Pro Tools, set the Kemper as the Master Clock, and your Apollo's clock source to S/PDIF, then you can record the purest digital signal. At any other sample rate or if Apollo is Master Clock, the Kemper will add additional latency.
- All tests done in Pro Tools with buffer size at 32 and sample rate at 44.1kHz.
- Kemper works internally at 44.1kHz, except for a few upsampled internal processes.
- If your project is not at 44.1kHz, then bounce a rough mix and import it to a new 44.1kHz session. Then, record your guitar tracks at 44.1kHz. Edit the tracks, and export at 44.1kHz/32 bit-float and use a good SRC like iZotope RX or Weiss Saracon to SRC your edited guitar tracks to your project's sample rate and import them back.
Here is the test (see Pro Tools project download at bottom 45MBish):
1 (BLUE)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? No
Playback Engine: Apollo
Synch: Kemper is master, Apollo is slave, method is S/PDIF
TRACK 1 (mono): Kemper "Direct Output" sends "DI Analog" to Neve DI via male TS cable, then into Apollo input 1
TRACK 2 (stereo): Kemper "Main Output" sends "Master Stereo" to Apollo inputs 3-4 via female XLR to male TRS cables
TRACK 3 (stereo): Kemper "SPDIF Output" sends "Master Stereo" to Apollo S/PDIF input
Results/Notes:
"DI Analog" is faster than "S/PDIF Output's" "Master Stereo" by 127 samples and "Main Output's" "Master Stereo" by 140 samples
2 (PURPLE)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? No
Playback Engine: Apollo
Synch: Kemper is master, Apollo is slave, method is S/PDIF
TRACK 1 (mono): Kemper "SPDIF Output" left sends "DI High/DI" to Apollo S/PDIF left input
TRACK 2 (mono): Kemper "SPDIF Output" right sends "Master Mono" to Apollo S/PDIF right input
Results/Notes:
"DI High/DI" and "Master Mono" have equal timing
3 (RED)
Device(s): Kemper Profiler Rack
Pro Tools Aggregate I/O? No
Playback Engine: Profiler
Synch: Kemper alone
TRACK 1 (mono): Kemper USB output 1 sends "DI High/DI" to computer
TRACK 2 (mono): Kemper USB output 2 sends "Master Mono" to computer
Results/Notes:
"DI High/DI" and "Master Mono" have equal timing
4 (GREEN)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? Yes
Playback Engine: Pro Tools Aggregate I/O
Synch: Kemper is master, Apollo is slave, method is S/PDIF, clock source is Kemper, drift correction is off
TRACK 1 (mono): Kemper "Direct Output" sends "DI Analog" to Neve DI via male TS cable, then into Apollo input 1
TRACK 2 (mono): Kemper "SPDIF Output" left sends "DI High/DI" to Apollo S/PDIF left input
TRACK 3 (mono): Kemper "SPDIF Output" right sends "Master Mono" to Apollo S/PDIF right input
TRACK 4 (mono): Kemper USB 1 sends "DI High/DI" to computer
TRACK 5 (mono): Kemper USB 2 sends "Master Mono" to computer
Results/Notes:
"DI Analog" is ahead of "S/PDIF Output" left's "DI High/DI" by 127 samples and USB 1's "DI/DI High" by 185 samples, clearly S/PDIF is superior to USB in terms of latency
"DI High/DI" and "Master Mono" have equal timing in S/PDIF and USB respectively
5 (YELLOW)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? Yes
Playback Engine: Pro Tools Aggregate I/O
Synch: Kemper is master, Apollo is slave, method is audio midi, clock source is Kemper, drift correction is on for Apollo
TRACK 1 (mono): Kemper "Direct Output" sends "DI Analog" to Neve DI via male TS cable, then into Apollo input 1
TRACK 2 (mono): Kemper "SPDIF Output" left sends "DI High/DI" to Apollo S/PDIF left input
TRACK 3 (mono): Kemper "SPDIF Output" right sends "Master Mono" to Apollo S/PDIF right input
TRACK 4 (mono): Kemper USB 1 sends "DI High/DI" to computer
TRACK 5 (mono): Kemper USB 2 sends "Master Mono" to computer
Results/Notes:
"DI Analog" is ahead of "S/PDIF Output" left's "DI High/DI" by 127 samples and USB 1's "DI/DI High" by 136 samples, USB performs better in 5 than 4 however clearly S/PDIF is still superior to USB in terms of latency
6 (ORANGE)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? Yes
Playback Engine: Pro Tools Aggregate I/O
Synch: Kemper is slave, Apollo is master, method is S/PDIF, clock source is Apollo, drift correction is off
TRACK 1 (mono): Kemper "Direct Output" sends "DI Analog" to Neve DI via male TS cable, then into Apollo input 1
TRACK 2 (mono): Kemper "SPDIF Output" left sends "DI High/DI" to Apollo S/PDIF left input
TRACK 3 (mono): Kemper "SPDIF Output" right sends "Master Mono" to Apollo S/PDIF right input
TRACK 4 (mono): Kemper USB 1 sends "DI High/DI" to computer
TRACK 5 (mono): Kemper USB 2 sends "Master Mono" to computer
Results/Notes:
"DI Analog" is ahead of "S/PDIF Output" left's "DI High/DI" by 200 samples and USB 1's "DI/DI High" by 197 samples, USB Beats S/PDIF slightly in this case, however USB still has more latency than the fastest S/PDIF in other cases
"DI High/DI" and "Master Mono" have equal timing in S/PDIF and USB respectively
7(turquoise)
Device(s): Kemper Profiler Rack and Universal Audio Apollo x6
Pro Tools Aggregate I/O? Yes
Playback Engine: Pro Tools Aggregate I/O
Synch: Kemper is slave, Apollo is master, method is audio midi, clock source is Apollo, drift correction is on for Kemper
TRACK 1 (mono): Kemper "Direct Output" sends "DI Analog" to Neve DI via male TS cable, then into Apollo input 1
TRACK 2 (mono): Kemper "SPDIF Output" left sends "DI High/DI" to Apollo S/PDIF left input
TRACK 3 (mono): Kemper "SPDIF Output" right sends "Master Mono" to Apollo S/PDIF right input
TRACK 4 (mono): Kemper USB 1 sends "DI High/DI" to computer
TRACK 5 (mono): Kemper USB 2 sends "Master Mono" to computer
Results/Notes:
"DI Analog" is ahead of "S/PDIF Output" left's "DI High/DI" by 127 samples and USB 1's "DI/DI High" by 234 samples, S/PDIF beats USB
CONCLUSION: S/PDIF is superior to USB in terms of latency when recording the Kemper digitally. Recording "DI Analog" while recording S/PDIF as in "1" may result in a lower quality DI because Apollo is using Kemper as its master clock instead of its own internal clock, exposing the Apollo to potential jitter. Instead, if you choose to record S/PDIF, record "DI/Master Left" and only use mono profiles (ie ones that null test; if you add phase inverted left channel to right channel you get no sound). The best way to record stereo profiles is via high quality analog connects such as XLR's (the 1/4" "Master Output" jacks are unbalanced TS unfortunately) with "Master Stereo" coming out of "Main Output" and "DI High/DI" coming out of "Direct Output."
Pro Tools Session: https://we.tl/t-0Nhl4W0lbA
, and please encourage others to do the same!