Hello Saleae Team,
There used to be a sampling rate of 125 kS/s in the Logic 1.x software.
Is it possible to bring it back to Logic 2?
Now I’m using the sampling rate of 781.25 kS/s instead, but it is a waste of RAM.
Thanks in advance!
Sampling rates lower than 781.25 kS/s should be available in the latest Logic 2.x software.
Can you let me know the following?
- What version of Logic 2.x are you running? Can you ensure you are running the latest version below?
Logic analyzer software from Saleae
- What are your capture settings (i.e. what channels are enabled)?
- Which Logic model do you own?
For example, here are the lowest sampling rates available for a single analog channel on Logic pro 16.
Thanks for your response.
I have a Logic Pro 16 and use the latest Logic 2.3.33.
Sorry for not being clear, I do have sampling rates lower than 781.25 kS/s.
The next choice is 31.25 kS/s, but in my use case I need a sampling rate of at least 100 kS/s.
In the Logic 1 software the 125 kS/s was an ideal choice, but now I have to use the 781.25 kS/s in Logic 2, which is a waste of RAM compared to Logic 1’s 125 kS/s sampling rate.
I can see that the sampling rates below 781.25 kS/s are different in Logic 1 and Logic 2.
So my question is: is it possible to make 125 kS/s available in Logic 2, too?
I can’t answer your actual question but I would like to bring up something. If you need 100k samples per second and you get 125k there might be a bit of aliasing in the sampling. For instance, if you wanted 100k because you have transitions at 10us boundaries then going to 125k is actually problematic as you get 8us sampling which means if you miss the signal on one sample boundary you’ll jitter by 8us. This isn’t actually any different from how a miss at 100k gives a 10us jitter. But, depending on the sampling rate you can somewhat be “scanning” through the time so to speak. If your sampling rate isn’t an even multiple of your needed precision then you scan around the signal transitions and that can cause random looking jitters. The logical analyzer doesn’t actually take up more RAM because of a higher sampling rate. It just records the transition times. So, if the signal isn’t transitioning any more often, a higher sampling rate leads to no more RAM usage. Only the oscilloscope function takes up more RAM. All that is to say, if 100k is your needed sampling rate I’d go with 500k and it’ll be just fine.
@tamas.csatari We currently don’t have any plans for providing new sampling rate options for Logic Pro 16.
@Collin brings up a great point below!
The logical analyzer doesn’t actually take up more RAM because of a higher sampling rate. It just records the transition times. So, if the signal isn’t transitioning any more often, a higher sampling rate leads to no more RAM usage. Only the oscilloscope function takes up more RAM.
For this reason, I’d recommend running at a higher sampling rate for digital channels specifically.
Mivel a rendszer eseményeket jegyez be, a mintavétel sebességétől független a memória felhasználás.
@timreyes OK, thanks for the info.
@Collin @sgyuri2003 In case of digital channels these are true. But I was bringing up the topic to find out whether it is possible to get back the “good old” 125 kS/s analog sampling rate like in Logic 1
Igen nálad a pont. Az analóg valóban valósan fogyasztja a memóriát.
Tamas via Saleae - Logic 2 <email@example.com> ezt írta (időpont: 2021. aug. 23., H, 10:03):
The Saleae Logic devices have fairly high oversampling rates for analog signals so the signal bandwidth you get for a 100kHz is likely to be lower than 20kHz (very hand wavy figure - Saleae can give you a better value). So you need to be sure that the signal information you want to record has no useful information above about 1/5 (hand wavy remember) the analyzer sample rate.
For modern computers the data rate needed and the memory required for recording anything below about 1MHz is trivial so an analog sampling rate below that doesn’t buy you much. Different perhaps if you are running on a Raspberry Pi or device of that sort, but in general a minimum rate of 1MHz should be fine.