# How to generate different noise in LTspice from run to run

I'm trying to simulate noise in my circuit, and ideally want to get a histogram of a certain parameter affected by that noise over many runs. However, when I use the white() command in LTspice, or variations of rand(), I get the same result from run-to-run. Is there a way to randomize the seed so that I get different white noise every iteration?

Thanks!

• This is a very interesting question and providing a histogram makes it seem like you're trying to predict noise in a circuit. I believe you could be getting the same results is because the simulations likely assume that the circuit is always initially untouched and unadulterated. I don't think there are options to provide a "seed" for your noise analysis. There's a similar question that's been asked here. Maybe that can help. – KingDuken Nov 25 '19 at 17:13
• Use the rand() to vary the starting point of your .tran simulation. – analogsystemsrf Nov 25 '19 at 17:25
• LTspice can read an external WAV file, though writing your own controllable noise generator and putting it in via a file seems a very clunky way of going about it. Similarly, you could create an m-sequence in the simulation. Several instances of white() delayed by different amounts and added together might get you sufficiently different noise simulations. – Neil_UK Nov 25 '19 at 17:26
• Use the .STEP card and create a LIST of values that you add to white(). Then each run would start at a different place in the sequence. Log data and process. You could also use a PWL file with .TRAN if you wanted to do make changes every so often to the base seed you use in white(), which might allow a single run to start at different "places" so that an overall accumulation appears like what you want. Also see this article. If you write what you need, perhaps a better answer? – jonk Nov 25 '19 at 18:41

You can use a combination of .step commands together with WHITE as shown below.