This means that either the source or sink experienced an xrun (= dropped
block). The sink automatically replaces the missing samples with
silence, hence the crackling.
Usually, xruns must be reported explicitly by the library user. This is
typically done to forward xruns reported by the audio backend. However,
there are two situations where xruns are caused and reported internally:
1. the process() method of AooSource or AooSink could not obtain a
reader lock. This should not never happen in Pd. If configured with
-DAOO_LOG_LEVEL=Debug, you should see a message "AooSource|AooSink:
process would block" in the terminal.
2. the process() method of AooSource could not write into the send
buffer. In that case you should see a message "AooSource: send buffer
overflow" in the terminal. If that happens, try to increase the send
buffer size by sending the "buffersize" message to the [aoo_send~]
object. The default send buffer size is 25 ms, which should be more than
enough on modern systems. If the network thread is slow or sometimes
hangs, a larger send buffer size might be necessary.
I should note that the AOO Pd externals are written with the assumption
of modern multi-core systems as they use separate threads for network
I/O to avoid blocking the audio thread. This could be a problem on
ancient systems like the SGI Octane.
Christof
On 7/11/2026 4:14 AM, Wolfgang Gaggl via Pd-list wrote:
What does it mean to get these messages when running aoo_send/receive~-help.pd:
aoo_receive~: block_xrun 127.0.0.1 9998 1 1
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