Forums

Digital Equalizer Design for a Radio Receiver

Started by Unknown February 7, 2006

Anonymous wrote:

> > I basically agree but you can minimize the fatigue on the listener by > getting rid of the noise bursts that occur as the fade drives the signal > towards the noise floor, right?
>
What you are trying to build is not the equalizer but the adaptive noise reduction. Yes you can get some perceptual improvement, however the sound will suffer "unnaturally deep" , "watery" and "rubber like" artifacts. Vladimir Vassilevsky DSP and Mixed-Up Signal Design Consultant http://www.abvolt.com
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message
news:A1uGf.54199$PL5.3648@newssvr11.news.prodigy.com...
> > > Anonymous wrote: > > > > > I basically agree but you can minimize the fatigue on the listener by > > getting rid of the noise bursts that occur as the fade drives the signal > > towards the noise floor, right? > > > > > What you are trying to build is not the equalizer but the adaptive noise > reduction. Yes you can get some perceptual improvement, however the > sound will suffer "unnaturally deep" , "watery" and "rubber like"
artifacts.
> > Vladimir Vassilevsky > > DSP and Mixed-Up Signal Design Consultant > > http://www.abvolt.com
So what do you think on an AM voice signal can be equalized?
Anonymous wrote:
> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:A1uGf.54199$PL5.3648@newssvr11.news.prodigy.com... > >> >>Anonymous wrote: >> >> >>>I basically agree but you can minimize the fatigue on the listener by >>>getting rid of the noise bursts that occur as the fade drives the signal >>>towards the noise floor, right? >> >>What you are trying to build is not the equalizer but the adaptive noise >>reduction. Yes you can get some perceptual improvement, however the >>sound will suffer "unnaturally deep" , "watery" and "rubber like" > > artifacts. > >>Vladimir Vassilevsky >> >>DSP and Mixed-Up Signal Design Consultant >> >>http://www.abvolt.com > > > > So what do you think on an AM voice signal can be equalized?
I can only begin to answer that if you explain what you want your equalizer to do. Volume? Frequency response? Phase distortion? Please tell me what you want to do. The name you give the gizmo that does it is unimportant. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
"Jerry Avins" <jya@ieee.org> wrote in message
news:1I2dndx7iPRC73fenZ2dnUVZ_tudnZ2d@rcn.net...
> Anonymous wrote: > > "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > > news:A1uGf.54199$PL5.3648@newssvr11.news.prodigy.com... > > > >> > >>Anonymous wrote: > >> > >> > >>>I basically agree but you can minimize the fatigue on the listener by > >>>getting rid of the noise bursts that occur as the fade drives the
signal
> >>>towards the noise floor, right? > >> > >>What you are trying to build is not the equalizer but the adaptive noise > >>reduction. Yes you can get some perceptual improvement, however the > >>sound will suffer "unnaturally deep" , "watery" and "rubber like" > > > > artifacts. > > > >>Vladimir Vassilevsky > >> > >>DSP and Mixed-Up Signal Design Consultant > >> > >>http://www.abvolt.com > > > > > > > > So what do you think on an AM voice signal can be equalized? > > I can only begin to answer that if you explain what you want your > equalizer to do. Volume? Frequency response? Phase distortion? > > Please tell me what you want to do. The name you give the gizmo that > does it is unimportant. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
I believe the original problem was modulation on his AM voice signal, i.e. fading was causing the volume at the speaker to waver.
Anonymous wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message > news:1I2dndx7iPRC73fenZ2dnUVZ_tudnZ2d@rcn.net... > >>Anonymous wrote: >> >>>"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message >>>news:A1uGf.54199$PL5.3648@newssvr11.news.prodigy.com... >>> >>> >>>>Anonymous wrote: >>>> >>>> >>>> >>>>>I basically agree but you can minimize the fatigue on the listener by >>>>>getting rid of the noise bursts that occur as the fade drives the > > signal > >>>>>towards the noise floor, right? >>>> >>>>What you are trying to build is not the equalizer but the adaptive noise >>>>reduction. Yes you can get some perceptual improvement, however the >>>>sound will suffer "unnaturally deep" , "watery" and "rubber like" >>> >>>artifacts. >>> >>> >>>>Vladimir Vassilevsky >>>> >>>>DSP and Mixed-Up Signal Design Consultant >>>> >>>>http://www.abvolt.com >>> >>> >>> >>>So what do you think on an AM voice signal can be equalized? >> >>I can only begin to answer that if you explain what you want your >>equalizer to do. Volume? Frequency response? Phase distortion? >> >>Please tell me what you want to do. The name you give the gizmo that >>does it is unimportant. >> >>Jerry >>-- >>Engineering is the art of making what you want from things you can get. >>&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095; > > > I believe the original problem was modulation on his AM voice signal, i.e. > fading was causing the volume at the speaker to waver.
The OP called it an equalizer; it's his explanation I want. AGC does a pretty good job of keeping the carrier level constant. Most of the volume change is caused by sidebands fading differently from the carrier. If the carrier only fades, the volume goes up and the signal gets distorted. There's no good way around that for music, but there are known methods for voice communications. Exalted carrier and audio AGC is a good way, but I wouldn't call that an equalizer. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
the carrier going down and sidebands fading differentially CAN be
corrected by an adaptive equalizer (not the same thing as an audio guys
call a graphic equlaizer)  that trys to keep the channel flat...this is
done all the time with QAM signals..... but my question was how do you
expect to be able to do this on a voice modulated carrier AM signal
that has no "expected" characteristics...For example, in the simplest
case, when there is no modulation, you have only carrier so there is no
way an AE can have any information about selective fading in the
channel....

OK maybe if some sort of low level pre-defined reference signal was
sent by the  Tx, but this is not done...
Mark

Mark wrote:
> the carrier going down and sidebands fading differentially CAN be > corrected by an adaptive equalizer (not the same thing as an audio guys > call a graphic equlaizer) that trys to keep the channel flat...this is > done all the time with QAM signals..... but my question was how do you > expect to be able to do this on a voice modulated carrier AM signal > that has no "expected" characteristics...For example, in the simplest > case, when there is no modulation, you have only carrier so there is no > way an AE can have any information about selective fading in the > channel.... > > OK maybe if some sort of low level pre-defined reference signal was > sent by the Tx, but this is not done...
In practice, one doesn't make it good, one settles for making it better. There's a lot of redundancy in voice that the brain can use if overall volume is held fairly level and distortion is avoided. Early exalted-carrier receivers had a sharp, narrow peak in the center of the IF, so that the carrier amplitude at the detector was 20 dB over 100% modulated sideband; this prevented most distortion from fading carrier. Modern practice achieves the same result by injecting a phase-locked oscillator. Various AGC schemes are used in the IF strip, but final AGC is done on the demodulated audio. The scheme wouldn't do for audiophiles, but it works for mobile dispatch. For the base station, diversity antennas provide even more improvement. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;