Member Avatar for Behzad Oskooi

Hi everybody


I have a project to record a telephone conversation.

My problem is that when I set the modem on recording condition, the voice of other side is being recorded but my own voice not recorded.

Please guide me what setting to be arranged to have both sides’ voices to be recorded.

type of Fax Modem is JUSTEC (Model JM56EA).


I initialized the modem for recording ,with below
instructions:

ATE0
AT+VSM=0,8000,0,0
AT+VGR=128
AT+VGM=128
AT+VLS=7
AT+VRX

bye

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  • Latest Post Latest Post by WolfPack

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As describes, only the far‑end voice is being saved while the local voice is missing. That behavior usually means the modem or the recording path is only presenting the receive channel to the recorder, not both directions. ’s reminder about consent is worth keeping in mind. was also correct: the modem voice documentation and vendor support are the right place to check for device‑specific behavior.

Try this diagnostic checklist first:

  • Verify the physical tap: confirm whether the modem is connected at the phone line jack or using a handset coupler. Handset pickups often see only the earpiece (far end) and miss your microphone.
  • Inspect how audio is exposed to the PC: some voice modems present transmit and receive as separate channels. Record in stereo and look at each channel separately to see which side is missing.
  • Test with different software/drivers: use another recording application or updated modem drivers to rule out software that only reads one stream.
  • Confirm modem voice capability: check the manual for full‑duplex or “both‑sides” recording support and any voice mode switches the firmware requires.
  • Use a controlled test: play a known tone from the remote side and speak locally; then analyze the saved file to see which signals are present.

If the modem cannot supply both channels simultaneously, the practical fixes are hardware: a proper line‑side hybrid or telephone recording interface (isolated line tap) mixes both transmit and receive and presents them to the PC safely. Do not connect a phone line directly to a sound card without proper isolation. If documentation is unclear, contact the modem vendor and ask specifically whether the voice interface supports bidirectional recording and how the driver exposes Tx/Rx buffers. Finally, confirm local legal requirements before recording calls.

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Member Avatar for Ancient Dragon

I don't know the answer, but I hope you realize that in many countries (like USA) recording telephone conversions is illegal unless (1) you have the permission of the person being recorded, or (2) you have a court order, or (3) you happen to be the President of the US (PM of England will probably do as well)

Member Avatar for Behzad Oskooi

thank you for your prompt reply
if i want do illegal operation, i could use Telephone Recording Adapter with price $51.95

Member Avatar for WolfPack

In any case your problem doesn't relate to C or C++. Please refer the modem documentation, or ask your question from the particular modem manufacturer's support staff.

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