Hello Stelios, >However, fldigi's default behaviour is to open the sound card at its >default (native) sample rate, usually 48 or 44.1 KHz, and then resample But how can you know the default native sample rate?
With Multidem, I can work in full duplex in any sampling speed from 8000 to 192000 Hz. I have noticed that you can open a 44.1 KHz at 48 KHz native sample rate sound card and reversely (the driver accepts all included 192 KHz). Of course, by working in full duplex, you rapidly see what is the true native sample rate (there are no "clicks" if you are on the good one and you can regulate the possible small shift between RX and TX sample rates). 73 Patrick ----- Original Message ----- From: "Stelios Bounanos" <[EMAIL PROTECTED]> To: <digitalradio@yahoogroups.com> Cc: "Tony" <[EMAIL PROTECTED]> Sent: Tuesday, September 30, 2008 3:03 PM Subject: Re: [digitalradio] Comparing data modes >>>>>> On Tue, 30 Sep 2008 00:04:19 -0400, Tony <[EMAIL PROTECTED]> said: > >>> What were the sampling rates used by each of those 5 applications, Tony? >>> 73, Dave, AA6YQ > >> The sample rates were 11025 Hz for Mixw and IZ8BLY MT63 terminal. Looks >> like >> 8000 Hz for DM780 and Multipsk. Not sure what's going on with Fldigi. I'm >> using the Vista version. > > The MT63 modem works at 8000 Hz as Simon noted. > > However, fldigi's default behaviour is to open the sound card at its > default (native) sample rate, usually 48 or 44.1 KHz, and then resample > to/from the modem rate using one of the converters from Erik de Castro > Lopo's excellent libsamplerate. The converter is chosen based on a > short speed test that is done the first time fldigi is run. On all > reasonably recent processors, that converter will be one of the "good" > SINC interpolators. It can always be changed later. > > We basically did this to avoid the not too uncommon situation where a > sound card/driver combination claims to support the modem's sample rate > only to return mangled audio. > > > To really open the sound card at the modem frequency, which is currently > 11025 Hz for Thor and DominoEX 5/11/22, and 8000 Hz for everything else, > use the Capture and Playback menus in the Audio settings. The default > value is Native (see above). Auto will try the modem rate first and, if > that fails, fall back to Native. You may want to try Auto if you know > that the OS can do better/faster resampling. > > The other options in those menus are the rates supposedly supported by > the sound card. I say "supposedly" because the driver may be telling > some slight fibs here, i.e., if it reports the hardware native rates > together with those that it can resample to in software. It's almost > certainly doing that if it lists every standard rate from 8KHz up to > 192KHz. > > Experience suggests that we can trust the default (native) sample rate, > at least on the cards and platforms tested so far. The other rates give > audio of uncertain quality. > > Anyway, if you force a rate that is different to the current modem's, > fldigi will need to resample. It will also resample, using the same > configured conveter, if the TX or RX ppm corrections are nonzero. Of > course it's smart enough to combine both kinds of resampling into one > step. > > > I don't know enough about Vista's audio system to be able to say what > happens if you run multiple programs that want different rates. > Possibly some of them will see slightly increased latency. > > Regarding CPU usage, you should make sure that you have enough CPU > cycles for everything; maybe aim to keep the system load at < 50%. > Fldigi can tell you if it's dropping audio because the CPU is too busy > but only in debug builds; perhaps something to change in a future > version. > > > 73, > Stelios, M0GLD. > > ------------------------------------ > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/sked > > 30M digital activity at http://www.projectsandparts.com/30m > > Recommended software : DM780, Multipsk, FLDIGI, Winwarbler ,MMVARI. > Yahoo! Groups Links > > > > >
