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Hello Rich,

This is a rather old email thread (2017) but it has been discussed many times in other threads.? There is a known issue around the Raspberry Pi and it's legacy USB stack with DIrewolf.? You're removal and re-install of the ALSA libraries fixing your issue is just coincidental and I'm pretty sure your issue remains though you don't realize it.?

Below is what I wrote about this topic in my Raspberry Pi documentation

--David
KI6ZHD




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?e. Direwolf Dead TX issue : OSS Support:

???? If you're using a USB based sound device (not an I2S-based sound device) on older Raspberry Pi
???? model (RPi 3B+, 3, 2, Zero-W, Zero, 1, but NOT the RPi4), there is a known issue of Direwolf
???? transmitting random amounts of "dead airtime" before actual modem sounds play.? You can read
???? more about this Raspberry Pi DWC bug at:

???????
?????????? and
???????
???????
???????

???? It was previously recommended that older Rpi HW owners try a work around using the OSS sound system
???? but this OSS support was accidentally removed from the Rpi kernel (recently re-added in).

???? Per , there are several options to address this
???? issue:

??????? Option #1: DWC2 USB stack - BETA RECOMMENDED
?????????????????? Rpi 0, 1, 2, 3, 3+ users can try using the alternative "DWC2" USB stack which the
?????????????????? Rpi 4 hardware already uses.? To try this, add the line "dtoverlay=dwc2" to the
?????????????????? /boot/config.txt file and rebooting.? Please make a backup of your SD card before
?????????????????? you try this

??????? Option #2: Use a cutting edge kernel version
?????????????????? Users running Raspberry Pi OS Buster, Stretch, and Jessie can switch to using the
?????????????????? bleeding edge kernels using the "rpi-update" tool to get both the DWC_OTG fixes
?????????????????? finally solve ALSA sound issues as well as bring the return of the OSS sound system.?
?????????????????? Once the 5.4.70 kernel for the Buster OS comes to a mainline release (~Jan 2021),
?????????????????? Raspberry Pi Buster users will no longer need the bleeding edge kernels.? The Stretch
?????????????????? and Jessie distros will NEVER get these fixes in a mainline kernel update so you'll
?????????????????? need to stick with the bleeding edge kernels.? Please make a backup of your SD card
?????????????????? before you try this.

??????? Option #3: Use the Legacy OSS sound stack
?????????????????? It seems that the original Linux sound system (OSS) is not affected by this DWC
?????????????????? USB issue and thus, fixes the issue.? The problem here is that in modern Raspberry Pi
?????????????????? OS versions, this option was accidentally disabled in the mainline kernel.? If users want
?????????????????? to go this route, you will either need to use a bleeding edge built kernel mentioned in
?????????????????? Option #2 above or compile your own kernel.? Building a new kernel isn't too hard
?????????????????? and there are many guides out there on the Internet how to do it but it does take time.
?????????????????? If you've never built a kernel, I recommend this as you'll learn a lot.


???? BETA RECOMMENDED Dead Airtime fix:?
?????????????????? For simplicity sake, I recommend users to try the DWC2 USB stack as it's very easy to
?????????????????? deploy but it doesn't have a huge amount of testing yet.? It's worth noting that this
?????????????????? is the same USB stack that's now used on all Raspberry Pi 4 and newer SBCs but it's just
?????????????????? not the default for them.?? To use this newer stack, it's highly recommended you FIRST
?????????????????? make a backup of your SD card if something goes badly.? See the later sections in this
?????????????????? guide how to do that easily.

?????????????????? With a SD backup done, simply edit the /boot/config.txt file and add the following line
?????????????????? to the bottom of the file:

????????????????????? dtoverlay=dwc2
?
?????????????????? Once done, reboot your Raspberry Pi and make sure everything is working fine.? That's it!
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