I'm observing an effect which needs explanation. Comments from the core developers will be appreciated. The effect was tested with versions 1.4.18 and today's master, on 64-bit Debian 7 and Ubuntu 14.04. All test calls were in PCMU or PCMA. My customer requested me to build a server for call quality assurance for their telephony system. I installed FreeSWITCH and set the following in the public dialplan to record the incoming audio: <extension name="record"> <condition field="destination_number" expression="^record_(.+)$"> <action application="jitterbuffer" data="60:200:20"/> <action application="set" data="RECORD_READ_ONLY=true"/> <action application="set" data="send_silence_when_idle=400"/> <action application="set" data="record_waste_resources=true"/> <action application="answer"/> <action application="record_session" data="/var/tmp/record_$1"/> <action application="playback" data="silence_stream://-1"/> </condition> </extension> The first try was with a DigitalOcean (KVM) virtual machine. I started recording *.wav files, and sometimes there were skipped frames: 1-2 skipped frames in a 2-minute call, one in every 10-15 calls. Then I changed the configuration to write raw audio files (removed the .wav extension from the record_session argument). As a result, the recorded input audio was quite bad: lost frames every few seconds in every call. Then I made test calls within the server itself, by originating a call to its public profile and playing the test WAV audio: fs_cli -x 'originate sofia/external/record_03@111.222.222.111:5080 &playback(/var/tmp/ITU-T_P_50_BRITISH_ENGLISH.wav)' The resulting input raw audio was also choppy. The same result was on another VM on a different physical server at DigitalOcean. Then I made the same self-call tests on a Xen VM and on a baremetal ARM server, and there the recorded audio was of perfect quality. Self-calls with recording into WAV files produced audio of perfect quality. Setting RECORD_USE_THREAD=false did not change the effect. Example of choppy received audio, converted from PCMU to WAV for convenience: http://www.k-open.com/s/record_04-in.wav The source audio: http://murmur.voxserv.ch/media/ITU-T_P_50_BRITISH_ENGLISH.wav So, it looks like the clock that is available at KVM is not precise enough, but that's not my question. QUESTION: why is raw recording so much more sensitive to the clock precision? thanks, stanislav