Hi All, The one REAL change in recent (PCI) sound cards seems to be that the input low pass filter AKA anti-aliasing filter HAS BEEN ELIMINATED on many (all?) of the cheaper PCI sound cards.
This can have SEVERE effects on the received spectra especially when a simple I&Q setup is used. These recent "cheap" PCI cards will seem VERY noisy. The simple solution, it seems to me, is to use an older ISA sound card!!? But you cannot just plug a ISA sound card into a PCI bus! So allowing Linrad to ship samples from one computer to another seems to me a VERY NICE idea. I can acquire the samples on a computer with ISA slots and then ship the samples to a faster PCI only computer for analysis and further processing. Thus bypassing the whole "cheap PCI" sound card issue. If you system seems 'very' noisy, I would suggest you try running linrad on an older computer with an ISA sound card. You may be VERY surprised with how much cleaner your spectra sound and look! Just my 2 cents. Happy holidays to all, john, ni1b On Sun, 17 Dec 2006, Leif Asbrink wrote: > Hi All, > > One aspect of the "digital culture" is that it silently > supplies what it thinks the user wants rather than > allowing the complexity of various decisions visible. > > One example is the choice of sampling speeds on soundcards. > > Old soundcards like Soundblaster 16 derive the sampling > speed from a master clock of fixed frequency and a number > that the user supplies to divide it by. This allows > arbitrary sampling speeds but one does not get exactly > what might be desired but something pretty close that > results from integer division. > > Modern cards may allow just a few sampling rates or even > just one (48kHz probably) and rate conversion is then done > in software. > > OSS had originally a good interface: One would send the > desired sampling rate to the device and in return one > would get the nearest actual sampling rate that the > hardware was capable of doing. Very good:-) > > It is different in Microsoft Windows however. Look > at the two images here: > http://www.sm5bsz.com/linuxdsp/install/uiparm.htm > > As it turns out Microsoft has won again. ALSA uses the > same strategy and OSS has changed to do it the same way. > BE VERY CAREFUL TO MAKE SURE YOU KNOW WHAT YOUR HARDWARE > IS DOING. Windows does not allow me to query the driver > for its native capability, neither does ALSA (as far as > I know) Only OSS has support for Linrad to know what the > proper speeds are. > > In OSS there is a parameter COOKEDMODE that will restrict > sampling speeds to only those supplied by hardware. > Linrad uses this only in the "U=Setup" menu so you can > edit the par_userint file manually and get rate conversion > by software in OSS easily if you wish to test it. > > I am curious about what might be behind this. I know > from OSS that their customers want the automatic rate > conversion. It does not look like a good idea to me. > Presumably the OSS customers are programmers who want > to avoid a complication (as they are used to under Windows). > I do not think the end users would be very happy if > they knew the consequences on performance..... > > It seems to me that this should be an issue for the > music industry. Do they really use non-integer > rate conversion in software? If not, why allow it - > and even make it standard? > > Are there some good stories on this subject? > > 73 > > Leif / SM5BSZ > > ############################################################# > This message is sent to you because you are subscribed to > the mailing list <linrad@antennspecialisten.se>. > To unsubscribe, E-mail to: <[EMAIL PROTECTED]> > To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> > To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]> > Send administrative queries to <[EMAIL PROTECTED]> > ############################################################# This message is sent to you because you are subscribed to the mailing list <linrad@antennspecialisten.se>. To unsubscribe, E-mail to: <[EMAIL PROTECTED]> To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]> Send administrative queries to <[EMAIL PROTECTED]>
