I did that one, just for kicks. Indeed, output tone is horrible. This is why they implemented a DTMF detector at the encoder side.. they detect the tones in the PCM signal, send them as digital sideband info, and filter out the actual tones. At the compressed output, the data frame has no more audio tones, but instead the DTMFDTCT flag is set, and two other fields contain the tone info.. --f
_____ From: [email protected] [mailto:[email protected]] On Behalf Of Woodrick, Ed Sent: Friday, May 15, 2009 4:58 AM To: [email protected] Subject: RE: [DSTAR_DIGITAL] Re: External D-Star encoding. And the 4800 bps has nothing to do with the bandwidth of the transmitted audio signal. The AMBE chip is very sophisticated in what it is sending. Just the name itself advanced multi-band is an indication that this isn't a PCM derived signal. Multi-band CODECs normally look at different bands of frequencies and send the information in each. So it is quite possible that much higher frequencies are sent. But it does sound like the chip focuses on the voice energy portion of the band. And this means that things such as tones won't do well across D-STAR. Take a linearly changing audio signal and stick it in, that's definitely not what you are going to get out. Ed WA4YIH From: [email protected] <mailto:dstar_digital%40yahoogroups.com> [mailto:[email protected] <mailto:dstar_digital%40yahoogroups.com> ] On Behalf Of John Hays Sent: Thursday, May 14, 2009 2:40 PM To: [email protected] <mailto:dstar_digital%40yahoogroups.com> Subject: Re: [DSTAR_DIGITAL] Re: External D-Star encoding. I'm not sure the 4800hz statement is correct. The data stream is 4800 bits per second which is put through GMSK before hitting the radio which requires a pretty flat response, which is why it is injected into the modulator directly (not through the audio chain) and pulled directly from the discriminator. I don't think the 4800bps directly maps to 4800hz. On May 14, 2009, at 10:42 AM, Jonathan Naylor wrote: > > > > Generally, is the encoded D-Star signal too delicate to feed over > a mic/speaker input/output (in the way that APRS is)? > > APRS is usually done with 1200Bd packet, which uses tones of 1200 > and 2200 Hz (I think), which fit nicely within the audio filters > that most radios have. D-Star uses a maximum frequency of 4800 Hz > and therefore wouldn't pass through those same audio filters. > > Jonathan G4KLX (working on a PC based D-Star system) > > . > > John Hays Amateur Radio: K7VE [email protected] <mailto:john%40hays.org> <mailto:john%40hays.org> [Non-text portions of this message have been removed] [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
