There are likely two possible areas for improvement and one where improvement is likely impossible. Some radios seem to have better transmit audio than others. Many people find the IC-2200 very good while many people find the ID-880 very bad. Possible the receive audio could also be improved by some additional audio processing. Much of the "poor" quality in DStar can be attributed to the AMBE Vocoder. This is a very complex algorythm that converts a high bit-rate voice data stream into a very low bit-rate data stream. By its very nature this is a lossy process. Removing bits must reduce the information content of the data. AMBE attempts to maximize the bit-rate while maintaining 'acceptable' audio quality. Some people may find the resulting sound unacceptable. Much like the battles over vinyl vd CD vs MP3 and tubes vs solid state in the music world, some ears are very sensitive to the aural content while others are quite insensitive. In a search to find a better sound for my 880, I contacted Bob, AB5N, who sells upgrades to a vatiety on ham microphones hoping he could provide a solution. below is his response. I hope it helps explain the problem. 73, Ted W1GRI Ted-
We have a conundrum here. Most people buy the ID-880H to use it on D-Star. Otherwise they would just buy a less-expensive rig. D-Star is a extremely compressed digital voice mode. They don't want to digitize any audio that isn't directly responsible for intelligibility. That passband is 300-3000... the old telephone response. Any audio that is outside that range would just be "wasting bits" encoding sound that does not help you understand what is being said. So, the mic audio is tailored narrowly to that passband for D-Star in the radio. Problem is, on FM, it sounds light at the bottom. If it was me, I would have had separate mic EQ circuits switched in for each mode. Thus, if we change the mic response curve to un-do what the mic pre-amp EQ's are doing, D-Star will go down the drain. Digital distortion is horrible. I've tried this experiment with my ID-800. I had to remove the new element and go stock again. As well, Icom engineers have always felt that their radios should have "communications-grade audio". None of their FM radios sound as pleasing as say a Yaesu FM mobile (totally analog radios). When you go to an Icom like a IC-7000, it is like comparing a vinyl record with a MP3. So, for radios that use the 133 or 131 - which do not have D-Star, indeed my mic element gives a very nice improvement. Uh oh... major storm here...tornado warnings.. I better unplug the router and laptop. Hope that clears it up... I wish I could help! Bob-AB5N _____ From: dstar_digital@yahoogroups.com [mailto:dstar_digi...@yahoogroups.com] On Behalf Of n2gyn Sent: Wednesday, September 01, 2010 14:27 To: dstar_digital@yahoogroups.com Subject: [DSTAR_DIGITAL] Re: Bit Rate? Thank you all for you reply and comments. Let me make myself clearer. I would like to see the audio quality of D-Star be improved. To MY ears' everyone sound like a robot. I thought this was due to the low bit rate. I am NOT impressed with the digital voice mode. I want to hear a more natural sounding voice. My telephone sounds better. How could this be achieved if not by bit rate? John ==================================================== --- In dstar_digital@yahoogroups.com <mailto:dstar_digital%40yahoogroups.com> , "Ted Wrobel" <twro...@...> wrote: > > Hi John, > > Not quite sure what you are thinking, but here is a brief overview of the > DStar data stream. > > The input to / output from the data processing 'module' of the radio is a > 9600 Baud stream - which equates to roughly 960 eight bit characters per > second. > > The logic of the system digitizes the voice in and passes it to the AMBE > Vocoder that compresses the data stream - a lot. > > It is the compresion by the Vocoder that is both the strength and weakness > of DStar. The compression makes a low data rate (and thus low bandwidth) > possible, but it also means that the re-constituted voice is an > approximation of the voice input. Generally the reconstructed voice is > pretty good, and given the bandwidth it is really quite remarkable. > > In any case, the baud rate of the system is fixed and cannot be modified at > any stage of the process without making the resulting stream unrecognizable > to other DStar systems. > > Note that the data rate over the internet can be much higher, but the chain > from repeater controller to / from the radio is fixed for DV comms at 9600. > > > 73 > Ted > W1GRI > > _____ > > From: dstar_digital@yahoogroups.com <mailto:dstar_digital%40yahoogroups.com> [mailto:dstar_digital@yahoogroups.com <mailto:dstar_digital%40yahoogroups.com> ] > On Behalf Of n2gyn > Sent: Tuesday, August 31, 2010 16:54 > To: dstar_digital@yahoogroups.com <mailto:dstar_digital%40yahoogroups.com> > Subject: [DSTAR_DIGITAL] Bit Rate? > > > > > Most radios are sent to 8bit. Can all radio's bit rate be changed? > I believe it is the LOW bit rate that lowers the quality of d-star's audio. > Is there a sub menu in the radio's. Also can the repeater's rate be change > to a higher rate? > John >
