Before I submit a bug report, I'm curious if others have experienced choppy sounding audio as well on the TRX-1 when monitoring P25 Phase 2 talkgroups.
Symptom: Speaker/headphone audio drops out very briefly about 3 times per second on more than half of the P25 Phase 2 transmissions, but these dropouts are not present in the TRX-1's recordings of the transmissions.
Discussion: The dropouts happen on precise 360 millisecond intervals and last 19 milliseconds (241 ms of audio followed by 19 ms of silence). When they are present they affect the entire transmission. They never begin or cease mid-transmission. I've found no rhyme or reason as to why they affect some transmissions but not others, and have tested it on two separate p25 phase 2 systems with identical results. (Both Phase 2 systems tested were simulcast systems.) Phase 1 talkgroups on those systems are unaffected.
The dropouts are clearly visible in the Audacity waveform screen capture at this link:
https://www.dropbox.com/s/zkhuz6xgw...rnal-record-vs-headphone-jack-record.jpg?dl=0
The top track in the capture was recorded using the TRX-1's internal recorder, and the lower track with dropouts was recorded by Audacity from the headphone jack.
The audio file depicted in the screen capture can be heard at the following link:
https://www.dropbox.com/s/hlozwo8ma6u6al6/Phase2-Internal-vs-External_Record.mp3?dl=0
The internal recording is on the left channel and the Audacity recording from the headphone jack is on the right.
This audio file contains a longer, 50-second sample of the choppy audio as recorded from the headphone jack.
https://www.dropbox.com/s/iz4dpo61me6te9n/Phase2AudioSample.mp3?dl=0
I read somewhere that P25 Phase 2 data streams utilize a "superframe" which is 360 milliseconds in length. This leads me to speculate that when the problem occurs, the TRX-1 squelch gate may be erroneously closing at the end of each superframe. Note that these experiments were all conducted with the squelch knob fully open (counterclockwise), and that its position had no impact on the dropouts.
I also monitored the dropouts while simultaneously tracking the P25 system on Unitrunker to see if there was any correlation with certain channels or time slots, or with other activity on the system. I found none. Even when the conversation remained on the same channel and time slot, often one transmission would be choppy and the reply would be fine, or vise versa.
Location or position of the scanner also had no impact, and there were no active priority channels. The fact that the TRX-1 audio recordings are unaffected would seemingly rule out reception problems.
I first noticed this problem in December 2016 after a firmware upgrade, but I had only used the scanner a very short time and don't know for sure whether it had been present before the upgrade. At first I assumed it to be LSM distortion, but that does not appear to be the case.
Greg
Symptom: Speaker/headphone audio drops out very briefly about 3 times per second on more than half of the P25 Phase 2 transmissions, but these dropouts are not present in the TRX-1's recordings of the transmissions.
Discussion: The dropouts happen on precise 360 millisecond intervals and last 19 milliseconds (241 ms of audio followed by 19 ms of silence). When they are present they affect the entire transmission. They never begin or cease mid-transmission. I've found no rhyme or reason as to why they affect some transmissions but not others, and have tested it on two separate p25 phase 2 systems with identical results. (Both Phase 2 systems tested were simulcast systems.) Phase 1 talkgroups on those systems are unaffected.
The dropouts are clearly visible in the Audacity waveform screen capture at this link:
https://www.dropbox.com/s/zkhuz6xgw...rnal-record-vs-headphone-jack-record.jpg?dl=0
The top track in the capture was recorded using the TRX-1's internal recorder, and the lower track with dropouts was recorded by Audacity from the headphone jack.
The audio file depicted in the screen capture can be heard at the following link:
https://www.dropbox.com/s/hlozwo8ma6u6al6/Phase2-Internal-vs-External_Record.mp3?dl=0
The internal recording is on the left channel and the Audacity recording from the headphone jack is on the right.
This audio file contains a longer, 50-second sample of the choppy audio as recorded from the headphone jack.
https://www.dropbox.com/s/iz4dpo61me6te9n/Phase2AudioSample.mp3?dl=0
I read somewhere that P25 Phase 2 data streams utilize a "superframe" which is 360 milliseconds in length. This leads me to speculate that when the problem occurs, the TRX-1 squelch gate may be erroneously closing at the end of each superframe. Note that these experiments were all conducted with the squelch knob fully open (counterclockwise), and that its position had no impact on the dropouts.
I also monitored the dropouts while simultaneously tracking the P25 system on Unitrunker to see if there was any correlation with certain channels or time slots, or with other activity on the system. I found none. Even when the conversation remained on the same channel and time slot, often one transmission would be choppy and the reply would be fine, or vise versa.
Location or position of the scanner also had no impact, and there were no active priority channels. The fact that the TRX-1 audio recordings are unaffected would seemingly rule out reception problems.
I first noticed this problem in December 2016 after a firmware upgrade, but I had only used the scanner a very short time and don't know for sure whether it had been present before the upgrade. At first I assumed it to be LSM distortion, but that does not appear to be the case.
Greg