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FreeDV Audio

Peter BentleyPeter Bentley Member
edited March 2017 in FLEX-6000 Signature Series

I have had a number of QSO's using FreeDV on a Flex6700 and I am very grateful to FlexRadio and the codec developers for the time and effort put into this project, it has a lot of interesting potential.

I would like to make the following comments:

If the aim on your radio is to make a readable transmission using the narrowest RF bandwidth over a wide range of signal strengths, then it currently does a good job and shows a massive advantage over SSB for audio signal to noise ratios on weak signals.

However, if you want to take advantage of the 6000 series ability to produce the finest transmit audio quality around, then it has a long way to go yet in terms of development.

Currently, using a full 3 kHz TX audio bandwidth, and high quality 5 channel digital audio processing, you can produce using SSB, an undistorted clarity and intelligability of audio rivalling AM and approaching that of FM.

Whilst an RF bandwidth of 1400Hz on DV is a great achievement, it would be nice to hope that as the mode develops we might be able to improve the resulting audio bandwidth to around 4.5 kHz, whilst still maintaining an RF envelope somewhat less than the normally accepted 3.0 kHz.

G4BIM Isle of Wight   U.K. 


  • Bob - G3WKWBob - G3WKW Member
    edited May 2015
    Hi Peter, thanks for the QSO yesterday. I said this was my first on the 6300 using FreeDV, but I had previously used the FreeDV application via DAX which was quite challenging given the number of different levels that have to be tweaked. FreeDV is not unique to Flex radios and is a major project with its own newsgroup at https://groups.google.com/forum/m/#!s... which would perhaps be the better place to voice your comment, after reading the earlier comments. The balancing of quality against bandwidth is Always a compromise and source of disagreement. The last time I used the FreeDV app there were a couple of incompatible choices available and the "standard" was still evolving. Though I subscribe to the group I have not been following in detail but I know ther is ongoing discussion about a VHF mode which would have better audio quality at the cost of higher bandwidth. One of the drawbacks of FreeDV with conventional radios has been the need to have 2 sound cards in the computer. With Flex an DAX that was not needed and there is a lot of effort on producing a stand alone microphone for conventional radios. This page http://www.rowetel.com/blog/?page_id=452 is worth reading and note that the main objective is "to make FreeDV better than SSB"

    Bob G3WKW
  • Peter BentleyPeter Bentley Member
    edited May 2015

    Thanks for your comments and input Bob, we both await the development of this with great anticipation I think.

    Best wishes

    Peter G4BIM

  • Steve-N5ACSteve-N5AC Community Manager admin
    edited February 2017
    Peter I agree with Bob's comments and we also would like to see a "switch" in the mode that would allow for a wider bandwidth with better audio, but a reduced SNR (necessarily) that could be used to get better audio when band conditions are good.  I agree you should make this comment to the FreeDV crew directly.
  • Peter BentleyPeter Bentley Member
    edited May 2015
    Thank you Steve, I will do that
  • Mike W9OJMike W9OJ Member ✭✭
    edited March 2017
    All the stations I've copied have a definite digital (and not in a good way) audio quality.
    The sound suggests a speech impediment similar to someone who has suffered a ****.
  • Mike - AG6BFMike - AG6BF Member
    edited May 2015
    I have noticed that mic settings make a large difference in the quality of the audio. I was monitoring a QSO where the Ham was changing both the mic and equalizer and difference was quite substantial. The quality was very poor to crisp and clear dependent only on the audio input.
  • Kevin WB4AIOKevin WB4AIO Member
    edited December 2016
    Currently, when band conditions warrant, I run ESSB on my Flex at 7.5 kHz audio bandwidth, and, when both stations have a good signal-to-noise ratio, the results are superior to even excellent broadcast reception. A worthy goal for the DV folks would be to have a mode available that gives us that amount of audio bandwidth, and a bit rate high enough on the digital side which gives us no more audible digital artifacts than does a 128 kbps mp3 stereo music file.

    I think that's achievable -- given that even in the early days of dial-up Internet, we were squeezing 48 kbps out of a copper landline.

    All the best,

  • Peter BentleyPeter Bentley Member
    edited May 2015

    You are singing my song Kevin....

    thank you


  • VernVern Member
    edited May 2015
    Have a 6500. All appears to be working except no audio. After calling a certain station his response (don't know to whom) was  "I hear a station but detected very very weak audio".  Thought it could be me. Any hints are accepted.
  • Peter BentleyPeter Bentley Member
    edited May 2015

    I have now tested this mode to death over the last week or so.

    Yes it works....just.

    If they concentrated only making use of the brilliant Flex technology to produce wonderful digital audio and didn't try to cram too much into the tiniest RF bandwidth, then we would have on HF, a great new product/mode.

    I sent the following E-Mail to the digitalvoice google group last week, so far no acknowledgement or comment.

    Thank you for the work you have done on the mode so far, I am using a FlexRadio 6700.

    I am very happy to make a donation.

    Could you please indicate if we might look forward in the near future to a second release which would allow a wider transmit audio bandwidth.

    I would imagine we could achieve transmitted audio of up to 4.5 kHz with a codec producing an RF transmit bandwidth stiil well below 3 kHz

    For me the mode is 'Parked'. I live in hope.


  • Bob - G3WKWBob - G3WKW Member
    edited May 2015
    I just watched this 36 minute video of a presentation just given by David Rowe. The last 6 or 7 minutes give a nice overview of the future roadmap of FreeDV.
  • Peter BentleyPeter Bentley Member
    edited May 2015

    Thanks for that Bob, it gives a good impression of the way this going.

  • DVDV Member
    edited August 2015
    Trying to install FreeDV,  Installed the Flex waveform manager, saw that FreeDV was in the window. Highlighted it and clicked install. Selected the Free.ssdr_waveform.  Initially, could not find FDV as a selectable item on my slice, but found it on the RX panel. Selected FDV, tuned to 14.236 and saw a FreeDV station on the panadapter, however no audio could be heard. I can hear the audio in the SSB mode, however in FDV it's completely silent.  Any advice from those that have FDV working? If you get it working for RX, does it also work conventionally in TX mode?
  • Bob - G3WKWBob - G3WKW Member
    edited August 2015
    There is a new mode of FreeDV in use (700? ) and I had the experience you describe first time I saw it. Had to resort back to the FreeDV application in order to decode. This is the risk of adding a mode that is itself still evolving. Hopefully someone will add the newer mode in due course but I am sure there will be further changes.

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