Recall that radio stations have call in programmes. During those phone in programmes a caller/listener would call the radio station from his house or vehicle and hear himself on the radio station. This causes feedback which is a nuisance to the radio dj on air. Now I am thinking of coming up with a system that would do away with that feedback, regardless of the distance from which the caller is calling from. Does someone have an idea, please help. Thank you
Feedback Cancellation
Started by ●July 24, 2006
Reply by ●July 24, 20062006-07-24
On Mon, 24 Jul 2006 08:50:24 -0500, "Pat" <chagondapat@yahoo.com> wrote:>Recall that radio stations have call in programmes. During those phone in >programmes a caller/listener would call the radio station from his house >or vehicle and hear himself on the radio station. This causes feedback >which is a nuisance to the radio dj on air. > >Now I am thinking of coming up with a system that would do away with that >feedback, regardless of the distance from which the caller is calling >from. Does someone have an idea, please help. > >Thank you >The problem is not so much feedback as it is delay. The caller is waiting to hear his voice from the radio, but due to the delay, is confused, or unsure if he is on the air. When he does hear his voice it out of sync and that causes further confusion. Consequently he speaks in fits and starts. A human factors problem, not a DSP problem. Greg Knox
Reply by ●July 24, 20062006-07-24
"Greg" <gdk1@bellsouth.net> wrote in message news:kam9c21n3t1nvgdr2q5ac5n6ep74skdj3f@4ax.com...> On Mon, 24 Jul 2006 08:50:24 -0500, "Pat" <chagondapat@yahoo.com> wrote: > > >Recall that radio stations have call in programmes. During those phone in > >programmes a caller/listener would call the radio station from his house > >or vehicle and hear himself on the radio station. This causes feedback > >which is a nuisance to the radio dj on air. > > > >Now I am thinking of coming up with a system that would do away with that > >feedback, regardless of the distance from which the caller is calling > >from. Does someone have an idea, please help. > > > >Thank you > > > > The problem is not so much feedback as it is delay. The caller is waiting > to hear his voice from the radio, but due to the delay, is confused, or > unsure if he is on the air. When he does hear his voice it out of sync and > that causes further confusion. Consequently he speaks in fits and starts. > > A human factors problem, not a DSP problem. > > Greg Knox >True. Delay is the problem. However, if it was feedback, this little box would be a COTS solution: http://www.behringer.com/DSP1124P/index.cfm?lang=ENG I picked one up a couple of months ago to kill a terrible resonance problem in my sound system (in the bathroom <g>). Of course, first thing out of the box, we put it on an audio FFT analyzer to check S/N, distortion, and filter shapes. We started scratching our heads about why the output level was so low: we were putting in a sine at 1Vp-p and only getting 8mV out. WTF? Answer: it defaults to "feedback destroyer" mode. It saw our sine wave as a feedback problem and did its best to destroy it. :-) Not bad for less than $100 US. Bob the bathroom sounds GREAT!
Reply by ●July 24, 20062006-07-24
Pat wrote:> Recall that radio stations have call in programmes. During those phone in > programmes a caller/listener would call the radio station from his house > or vehicle and hear himself on the radio station. This causes feedback > which is a nuisance to the radio dj on air.I believe they will always have a delay long enough to keep bad words off the air. Still, one must keep the echo off the air.> Now I am thinking of coming up with a system that would do away with that > feedback, regardless of the distance from which the caller is calling > from. Does someone have an idea, please help.I once knew someone working on a system using double balanced mixers with something like a 1Hz mixer input. I never heard the results, but I don't remember that it worked very well. If you arrange it to add 1Hz to any signal coming in, that would affect the feedback, and maybe not change a voice signal too much. -- glen
Reply by ●July 25, 20062006-07-25
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message news:KqSdnWdm96su2ljZnZ2dnUVZ_rudnZ2d@comcast.com...> Pat wrote: > > > Recall that radio stations have call in programmes. During those phonein> > programmes a caller/listener would call the radio station from his house > > or vehicle and hear himself on the radio station. This causes feedback > > which is a nuisance to the radio dj on air. > > I believe they will always have a delay long enough to keep bad words > off the air. Still, one must keep the echo off the air. > > > Now I am thinking of coming up with a system that would do away withthat> > feedback, regardless of the distance from which the caller is calling > > from. Does someone have an idea, please help. > > I once knew someone working on a system using double balanced mixers > with something like a 1Hz mixer input. I never heard the results, but > I don't remember that it worked very well. If you arrange it to add 1Hz > to any signal coming in, that would affect the feedback, and maybe not > change a voice signal too much. > > -- glen >All you need to do is phase -advance the signal. M.P -- Posted via a free Usenet account from http://www.teranews.com
Reply by ●July 25, 20062006-07-25
glen herrmannsfeldt wrote:> I once knew someone working on a system using double balanced mixers > with something like a 1Hz mixer input. I never heard the results, but > I don't remember that it worked very well. If you arrange it to add 1Hz > to any signal coming in, that would affect the feedback, and maybe not > change a voice signal too much.Up to 5 Hz is OK for most voices. I built a tube version that worked using filtering, not phasing. The biggest problem was keeping the up- and down-converters from pulling one another. With the best power-supply filtering and other isolation I could manage, 2 HZ was impossible. # Hz worked, but I didn't trust it for long-term stability. 4 Hz was solid, but 5 Hz gave better feedback-suppression and still sounded all right, so I used it. Home Depot and others use a different system altogether. They have a digital recording chip in the PA connected to the phone, and nothing comes out of the speaker until the phone is hung up. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 25, 20062006-07-25
Thank you ladies and gentlemen for your responses. Well I will try the adding of 1Hz to 5Hz and also will try the phasing ideas. In this case all ideas are worth trying out. As for the problem being delay, I have heard feedback coming out when a caller calls the radio station while the volume of their radio receiver is high. That's my concern. Some callers can call from long distances while some would call from within the same town with the radio station, how do I manage the feedback control and callers are from different places, say the distances of up to 1600km. We know the delays of telephone lines and microwaves depend on the distance. Theproject is manageable for the same distances like in a conference room but I am stuck in this case. I thank you once again
Reply by ●July 25, 20062006-07-25
Jerry Avins wrote:> ... With the best power-supply > filtering and other isolation I could manage, 2 HZ was impossible. # Hz > worked, but I didn't trust it for long-term stability. 4 Hz was solid, > but 5 Hz gave better feedback-suppression and still sounded all right, > so I used it.Note that # = <shift>3 :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 25, 20062006-07-25
Pat wrote:> Thank you ladies and gentlemen for your responses. > > Well I will try the adding of 1Hz to 5Hz and also will try the phasing > ideas. In this case all ideas are worth trying out. As for the problem > being delay, I have heard feedback coming out when a caller calls the > radio station while the volume of their radio receiver is high. That's my > concern. > > Some callers can call from long distances while some would call from > within the same town with the radio station, how do I manage the feedback > control and callers are from different places, say the distances of up to > 1600km. We know the delays of telephone lines and microwaves depend on the > distance. Theproject is manageable for the same distances like in a > conference room but I am stuck in this case. > > I thank you once againThe feedback that disturbs you is not entirely the same as what limits the gain in a PA system. Many advances have happened since I built the frequency shifter more than 50 years ago, and now there are better ways. Most talk-show hosts remind callers to turn their radio volume down, and that seems to suffice. Can you tell us what specific problem needs to be addressed? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●July 26, 20062006-07-26
">Pat wrote:>> Thank you ladies and gentlemen for your responses. >> >> Well I will try the adding of 1Hz to 5Hz and also will try the phasing >> ideas. In this case all ideas are worth trying out. As for the problem >> being delay, I have heard feedback coming out when a caller calls the >> radio station while the volume of their radio receiver is high. That'smy>> concern. >> >> Some callers can call from long distances while some would call from >> within the same town with the radio station, how do I manage thefeedback>> control and callers are from different places, say the distances of upto>> 1600km. We know the delays of telephone lines and microwaves depend onthe>> distance. Theproject is manageable for the same distances like in a >> conference room but I am stuck in this case. >> >> I thank you once again > >The feedback that disturbs you is not entirely the same as what limits >the gain in a PA system. Many advances have happened since I built the >frequency shifter more than 50 years ago, and now there are better ways.>Most talk-show hosts remind callers to turn their radio volume down, and>that seems to suffice. Can you tell us what specific problem needs to be>addressed? > >Jerry >-- >Engineering is the art of making what you want from things you can get."My objective is to completely do away with the talk show hosts asking the caller to turn down their volume. I want the caller to be free to talk and have their volume relatively up without causing negative feedbak. Thank you
