Kernel command line could be done with device tree, but by far the simplest way is to edit file “/boot/extlinux/extlinux.conf”. Find the “APPEND” key/value pair in “extlinux.conf”. Note that even if it line wraps it is a single long line, with parameters separated by a space. Simply add a space at the end of the line followed by " ASPCM=off".
You don’t really need to customize the kernel, but if you do, then check the “kernel customization” part of the R32.7.1 documentation.
https://docs.nvidia.com/jetson/archives/l4t-archived/l4t-3261/index.html#page/Tegra%20Linux%20Driver%20Package%20Development%20Guide/kernel_custom.html#
You would have to compile a new kernel which starts with the default configuration, set those values to “n” (no) after the default, then build and install both the kernel and the modules (after setting a “y” feature to “n” it is usually best to reinstall modules as well). You’ll want a new “CONFIG_LOCALVERSION”, and probably save the old kernel Image and add the new one as something like “Image-noaspcm” (and then the recommended “CONFIG_LOCALVERSION” would be “=noaspcm”).
You don’t need to work on the kernel if the command line is in place. You can verify the kernel command line has what you want via “cat /proc/cmdline”.