Tom :
Your categories are rather broad to me, if we are just talking about audio. Telecomm channels might care about group delay simply to allow V.xx dialup modems, FAX, Caller ID etc. Digital transmission systems might care about group delay if the modulation is some form of PSK or QAM regardless of whether the system is carrying voice or data. Analog TV might care about group delay because it is a combination of FM, PM and AM. I entirely agree that you won't hear the difference between Alberto's audio samples. I'd venture to guess the group that understands this question best are the audio coding experts. There is no audio codec that attempts to preserve phase information, as it was determined long ago that it makes no difference to the ear. Chuck _____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Holden Sent: Friday, February 02, 2007 7:56 PM To: [email protected] Subject: Re: [soft_radio] Re: Tecnical discussion I could not hear a difference on my notebook's poor sound system that would allow me to pick out which was which but I don't think we would hear any anyway on a simple steady-state signal such as this. It's a poor example. Group delay distortion is more discernable on transients and more complex waveforms. Why do finer multi-driver speaker systems attempt to time-align the drivers? Why do telecommunications systems control group delay on speech channels? Why is group delay controlled in analog television systems, in digital transmission systems? Because it can be a discernible and objectionable distortion if it's large enough and the signal or information is susceptible to it. But group delay does not generate new components in the signal - it just shifts them around in time. New waveform but the component frequencies and amplitudes are unchanged. I agree that the assertion misstates the nature of group delay distortion. Tom VE3MEO ----- Original Message ----- From: i2phd To: [EMAIL PROTECTED] <mailto:soft_radio%40yahoogroups.com> ups.com Sent: Friday, February 02, 2007 7:10 PM Subject: [soft_radio] Re: Tecnical discussion --- In [EMAIL PROTECTED] <mailto:soft_radio%40yahoogroups.com> ups.com, "in3otd" <[EMAIL PROTECTED]> wrote: > > Maybe someone on the group who is less programming impaired than me > could synthetically generate an SSB signal demodulated with different > phase shifts to see if the differences can be heard... > > Best regards, > > Claudio, IN3OTD > Claudio, no need to program anything to hear (or to not hear...) the differences between two sounds with components of different phases. I generated with Adobe Audition a sound file with a 800 Hz tone, summed with its second harmonic at 1600 Hz, which had 0 degrees of phase difference at time 0 (arbitrarily chosen). Then I did the same, but now the phase difference at time 0 was 90 degrees. I prepared a simple Web page where it is possible to see the two waveforms (quite different one from the other) and to hear them. To my ears they sound _exactly_ the same. The page is at http://sundry. <http://sundry.i2phd.com/phase.html> i2phd.com/phase.html This means that the following assertion probably is not valid : 5) If we put a multiple monochromatic signal in a system with flat response, linear amplitude response and NOT flat group delay, will the signal be distorted ? YES .NEW SIGNALS (DISTORTION )WILL BE CREATED FROM THE GROUP DELAY BEING NOT FLAT ,LIKE WHEN THERE IS ONLY NON LINEAR AMPLITUDE RESPONSE . 73 Alberto I2PHD [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
