The Cacophony of Digital Voice Continues (Part 2)

Digital transmissionThis post is a continuation of The Cacophony of Digital Voice Continues (Part 1), so you probably should read that one first.

All of the popular amateur digital voice (DV) systems (D-STAR, DMR and YSF) use the AMBE vocoder (voice codec) technology. This technology was developed by Digital Voice Systems, Inc. and is proprietary technology covered by various patents. The use of proprietary technology on the ham bands causes some folks to get worked up about it, especially proponents of an open source world. See my blog posting: Digital Voice at Pacificon and this presentation by Bruce Parens K6BP: AMBE Exposed. Codec2 is an alternative open voice codec developed by David Rowe, VK5DGR. David is doing some excellent work in this space, which has already produced an open codec that is being used on the ham bands. FreeDV is an umbrella term for this open codec work. Here’s a recent video of a presentation on FreeDV by VK5DGR.

It will be interesting to see if and how Codec2 gets adopted in a DV world already dominated by AMBE. After all, a new codec is another contributor to the digital cacophony. On the HF bands, it is easier to adopt a new mode if it can be implemented via a soundcard interface (which FreeDV can do). Any two hams can load up the right software and start having a QSO. The same is true for weak-signal VHF/UHF via simplex. (Note that Flexradio also supports FreeDV, showing how Software Defined Radio (SDR) has an advantage with adopting new technology.)  VHF/UHF repeaters are trickier because you must have a solution for both the infrastructure (repeaters and networks) as well as the user radios.

The vast majority of digital repeaters support just one digital format. For example, a D-STAR repeater does not usually repeat DMR or YSF transmissions. Interestingly, DMR and YSF repeaters often support analog FM via mixed mode operation for backward compatibility. It is definitely possible to support multiple digital formats in one repeater, but the question is will large numbers of repeater owners/operators choose to do that? With existing DV systems, the networking of repeaters is unique to each format which represents another barrier to interchangeability. In particular, most of the DMR infrastructure in the US is MOTOTRBO, which won’t ever support D-STAR or YSF.

In the case of a new vocoder, we can think of that as just a new format of bits being transported by the existing DV protocol. DMR, for example, does not actually specify a particular vocoder, it’s just that the manufacturers developing DMR equipment have chosen to use AMBE technology. So from a technical viewpoint, it is easy to imagine dropping in a new vocoder into the user radio and having it work with other identical radios. Of course, these radios would be incompatible with the existing installed base. Or would they? Perhaps we’d have a backwards compatibility mode that supports communication with the older radios. This is another example of putting more flexibility into the user radio to compensate for DV incompatibilities.

One objection to AMBE is the cost of the technology, especially when compared to free. When D-STAR radios first started using AMBE codec chips, the chip cost was rumored to be $25 to $50, but I don’t have a solid source on that. Now, I see that Tytera is selling a DMR handheld at around $100, including AMBE technology inside, so the codec can’t be very expensive. If a free codec starts to be a credible threat, it will put additional pricing pressure on the AMBE solution.

A potential advantage of Codec2 is superior performance at very low signal-to-noise ratio. We’ve all experienced the not-too-graceful breakup of existing DV transmissions when signals get weak. Some of the Codec2 implementations have shown significant improvement over AMBE at low signal levels.


Repeating a key conclusion from Part 1:

  • For the foreseeable future, we will have D-STAR, DMR and YSF technologies being used in amateur radio. I don’t see one of them dominating or any of them disappearing any time soon.

Adding in these conclusions for Part 2:

  • Codec2 will struggle to displace the proprietary AMBE vocoder, which is well-established and works. The open source folks will promote codec2 but it will take more than that to get it into widespread use. Perhaps superior performance at low signal levels will make the difference.
  • Repeater owner/operators will continue to deploy single-DV-format repeaters. This will make multiformat radios such as the DV4mobile be very attractive. In other words, we will deal with the digital cacophony by having more flexible user radios. This will come at a higher price initially but should drop over time.

Repeating this one from Part 1:

  • A wild card here is DMR. It benefits from being a commercial land mobile standard, so high quality infrastructure equipment is available (both new and used gear). And DMR is being embraced by both land mobile providers (i.e., Motorola, Hytera) and suppliers of low cost radios (i.e., Tytera, Connect Systems). This combination may prove to be very powerful.

Well, those are my thoughts on the topic. I wish the DV world was less fragmented but I don’t see that changing any time soon. What do you think is going to happen?

73, Bob KØNR

8 Replies to “The Cacophony of Digital Voice Continues (Part 2)”

  1. Like most digital tech, there will be a shakeout and sooner or later stabilization.
    Segmented markets are hard to make money from, so someone will buy some out and a standard will evolve. It make take 5-10 years for enough economic pain to accumulate before this happens.

    • Hi Lauren,
      Some technologies roll out in a more orchestrated fashion, depending on the maturity of the industry. Typically, there is because a strong standards body handles competing views and crafts one standard (example: LTE for 4th generation mobile phones). The various generations of WiFi (802.11 variants) are another good example.

      Ham radio does not have that industry structure, so the different manufacturers are going it alone. This is another reason why DMR may be the wildcard.

      73, Bob

    • Yeah maybe. But P25 technology is not a great fit for ham use. It can be made to work though.

  2. One thing that does it exist now is MMDVM, a multi-mode digital voice modem. It allows one to retro fit an existing analog repeater into one that supports, D-Star, Yaesu System Fusion, DMR and P25.

    Prior to DMR becoming popular in ham radio, and Yaesu introducing their Fusion stuff, Codec 2 made some sense. At that point it was pretty much just D-Star, and everyone was in a tizzy about it using a propriety codec/vocoder. Now there are so many different VHF/UHF digital radios out there using the patented technology, and there still isn’t a drop in “open” replacement for VHF/UHF.

    A couple years ago Bruce Perens gave a pretty good history/background speech titled “AMBE Exposed” What we need now are some specifics (a follow up talk). He talked about trying to invalidate the patent based on David Rowe’s work and that DVSI made use of AMBE in commerce before their own patent applications.

    Presently Jonathan’s MMDVM (mutli-mode digital voice modem) repeater project has the capability to tie things together using multi-mode conference bridges. We have heard a little bit about a the CCS7 reflector system that is popular in Europe, that does just that to some extent too

    One thing that needs attention/work is presently all the hardware dongles to deal with AMBE can only process a single stream at a time. This is less than ideal for anyone interesting is hosting a multimode conference reflector system.

      • Open source projects like MMDVM are never done, as its open to further enhancements. Right now I think they are working to extend support beyond just the arduino due.. something like the tensy microcontroller, and there is work to redesign the interface board so it works better with a wider range of analog radios with less fuss.

  3. Pingback: After a long hiatus I’m back! | Colorado Ham Shack