Forums

Polyphase filter questions

Started by Unknown March 12, 2007
<redpathdu@yahoo.co.uk> wrote in message 
news:1174403295.380400.60650@l75g2000hse.googlegroups.com...
> Hi Fred, > > Finally got it fixed. Output waveforms look good, except for one > thing...the output, though spectrally correct is very low compared to > the input...there is a great deal of attenuation. Can this attenuation > be quantified? > > Duncan
You didn't say but I think it's probably a factor of "N" where N is the decimation factor. After all, (N-1)/N of the energy has been removed, leaving 1/N, by ignoring all but every Nth sample. Fred
Fred Marshall wrote:
> <redpathdu@yahoo.co.uk> wrote in message > news:1174403295.380400.60650@l75g2000hse.googlegroups.com... >> Hi Fred, >> >> Finally got it fixed. Output waveforms look good, except for one >> thing...the output, though spectrally correct is very low compared to >> the input...there is a great deal of attenuation. Can this attenuation >> be quantified? >> >> Duncan > > You didn't say but I think it's probably a factor of "N" where N is the > decimation factor. After all, (N-1)/N of the energy has been removed, > leaving 1/N, by ignoring all but every Nth sample.
Why doesn't the zero-order hold put the energy back? Suppose a 4 KHz bandlimited signal sampled at both at 8 KHz and at 44.1. Is there a difference in loudness when they're played back? Jerry -- Engineering is the art of making what you want from things you can get. &macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;
"Jerry Avins" <jya@ieee.org> wrote in message 
news:du-dnZHzAag4rpzbnZ2dnUVZ_rXinZ2d@rcn.net...
> Fred Marshall wrote: >> <redpathdu@yahoo.co.uk> wrote in message >> news:1174403295.380400.60650@l75g2000hse.googlegroups.com... >>> Hi Fred, >>> >>> Finally got it fixed. Output waveforms look good, except for one >>> thing...the output, though spectrally correct is very low compared to >>> the input...there is a great deal of attenuation. Can this attenuation >>> be quantified? >>> >>> Duncan >> >> You didn't say but I think it's probably a factor of "N" where N is the >> decimation factor. After all, (N-1)/N of the energy has been removed, >> leaving 1/N, by ignoring all but every Nth sample. > > Why doesn't the zero-order hold put the energy back? Suppose a 4 KHz > bandlimited signal sampled at both at 8 KHz and at 44.1. Is there a > difference in loudness when they're played back? > > Jerry
Jerry, It's not clear that the "waveform" he mentions is analog/continuous.... Fred
Fred Marshall wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message > news:du-dnZHzAag4rpzbnZ2dnUVZ_rXinZ2d@rcn.net... >> Fred Marshall wrote: >>> <redpathdu@yahoo.co.uk> wrote in message >>> news:1174403295.380400.60650@l75g2000hse.googlegroups.com... >>>> Hi Fred, >>>> >>>> Finally got it fixed. Output waveforms look good, except for one >>>> thing...the output, though spectrally correct is very low compared to >>>> the input...there is a great deal of attenuation. Can this attenuation >>>> be quantified? >>>> >>>> Duncan >>> You didn't say but I think it's probably a factor of "N" where N is the >>> decimation factor. After all, (N-1)/N of the energy has been removed, >>> leaving 1/N, by ignoring all but every Nth sample. >> Why doesn't the zero-order hold put the energy back? Suppose a 4 KHz >> bandlimited signal sampled at both at 8 KHz and at 44.1. Is there a >> difference in loudness when they're played back? >> >> Jerry > > Jerry, > > It's not clear that the "waveform" he mentions is analog/continuous....
Nevertheless, decimation lowers the sample rate and therefore the effective "duration" of each sample. Does a 100 HZ full-scale sinewave show more energy when sampled at 20 KHz than it does when samples at 500 Hz? Jerry -- Engineering is the art of making what you want from things you can get. &macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;&macr;