Hello everyone,
I recently picked up a Logic 8 for my Acoustic Emission experiments and have been really happy with the results.
However I currently have to move on to larger tests (1 hour or so) and I wish to have minimal downtime during the acquisition.
I have 2 Analog channels sampling at 2.5MS/s so my RAM gets crowded quite fast !
I read in the documentation the following 2 points.
- ''If you are recording analog, turn off the up-sample option" I could not find it. Is this only in old Logic software versions ?
- " Analog signal needs to be sampled 10 times faster than bandwidth" Is 2 times faster not enough ?
Also I tested for shorter tests (1GB data) and the time for saving the capture was not negligible compared to the acquisition time. Do you believe I could speed up the process with a custom python extension ?
I’m looking forward to your comments and wish you a great day.
Alexandre
@ableuset Glad to hear you’ve been happy with using Logic 8 so far. Some comments on your questions below:
- ''If you are recording analog, turn off the up-sample option" I could not find it. Is this only in old Logic software versions ?
This is actually just in the older Logic 1.x software. This option was there simply to improve waveform display and rendering performance. Rendering performance has been improved pretty drastically in Logic 2.x compared to Logic 1.x, so this setting isn’t necessary anymore.
- " Analog signal needs to be sampled 10 times faster than bandwidth" Is 2 times faster not enough ?
Sampling analog at 2 times the frequency of your signal is not enough if you want a reasonable approximation and reconstruction of the analog signal you are recording. For digital recordings, 2 times the frequency (Nyquist) is borderline for just avoiding aliasing. Though, our general rule of thumb is:
- Digital recordings be sampled at least 4x the frequency of the signal
- Analog recordings be sampled at least 10x the frequency of the signal
Also I tested for shorter tests (1GB data) and the time for saving the capture was not negligible compared to the acquisition time. Do you believe I could speed up the process with a custom python extension ?
I assume you are saving captures as per the instructions below?
Unfortunately, it’s not possible to improve this via a python extension. The performance is tied to our back-end. What kind of save times are you experiencing? Can you share a copy of your capture preset file? Also, what are your PC specs? As a first step, I’d like to see if the capture save times you are seeing are within what we expect.
Hello Tim,
Thank you for your answer, I will make sure next time I do an experiment to use more adequate sampling speed !
For now, I have just saved the recordings following File > Save Capture. (using default preset)
The last test I did was roughly 1 GB, took 86 seconds to record and 35 seconds to write on the disk. I looked at the performance window during the save and the CPU activity was very low.
The computer I use is a i5-8350U with 16GB of ram.
If I could reduce the saving time it would be perfect !
@ableuset I’d be happy to run some tests on our PCs using your same setup to see if the save times are in line with what we would expect. Feel free to share your Capture Preset file with me as per the link I shared previously and we can take a look!
@ableuset Apologies, I just noticed you said that you used the default preset. I ran a quick test on my end and the Save Capture time took roughly 7 seconds after an 86 second capture with the default preset (approximately 1GB RAM usage as well).
I tested it on an i7-7920HQ (Also 4-cores / 8-threads). What is the make/model of your computer? I’m wondering if some sort of low-power mode is in effect since you mentioned that CPU activity was very low during that time.
Saving is likely to be I/O bound so will depend much more on hard drive performance than processor. If one machine is using spinning iron and the other a SSD then a factor of 10 performance difference is quite likely. If the write is across a network save times could be another factor of 10 slower.
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Hi Tim and Peter.
The model is a Dell Latitude 5490, but I will try on my personal computer which is much better. 7 seconds would be perfect !
Its running with an SSD not a HDD, but as you said its probably due to a low power mode … I will try to change the power settings (if I can)
Thanks again for your kind inputs
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