hi ppl, Please help me with this problem I got stuck at during my DSP project: I am getting a transmission along a channel and I have to tell whether it is speech (LPC coded say) or FAX transmission. The sender of the transmission is anonymous so, I have no info from him. Are there any unique or invariant properties in a fax transmission that can be used for this purpose? Thanks in advance. vsp IIT Delhi
distinguish between fax and speech
Started by ●January 24, 2006
Reply by ●January 24, 20062006-01-24
VSP wrote:> hi ppl, > Please help me with this problem I got stuck at during my DSP project: > > I am getting a transmission along a channel and I have to tell whether > it is speech (LPC coded say) or FAX transmission. The sender of the > transmission is anonymous so, I have no info from him. Are there any > unique or invariant properties in a fax transmission that can be used for > this purpose? > Thanks in advance. > > vsp > IIT Delhi > >Is not a "fax transmission" just a modem protocol using a few specific tones? I answer vaguely for two reasons: 1. OP may be a student who needs guidance in how to formulate his problem/question. 2. I've exhausted my knowledge of the subject and am not ashamed to admit my limitations [ Hi VV, snicker snicker ;]
Reply by ●January 26, 20062006-01-26
>VSP wrote: > >> hi ppl, >> Please help me with this problem I got stuck at during my DSP project: >> >> I am getting a transmission along a channel and I have to tell whether >> it is speech (LPC coded say) or FAX transmission. The sender of the >> transmission is anonymous so, I have no info from him. Are there any >> unique or invariant properties in a fax transmission that can be usedfor>> this purpose? >> Thanks in advance. >> >> vsp >> IIT Delhi >> >> > >Is not a "fax transmission" just a modem protocol using a few specific >tones? > >I answer vaguely for two reasons: > 1. OP may be a student who needs guidance in how to formulate his > problem/question. > 2. I've exhausted my knowledge of the subject and am not ashamed to > admit my limitations [ Hi VV, snicker snicker ;] > >hi first, thx for your reply Mr.Richard Owlett. Could you or anyone else atleast tell me a good online source where i can read about how the FAX data to be transmitted is exactly coded. Again, i am trying to look for a property in this coding that would help me distinguish it from other transmissions eg some kind of periodicity in the coded signal etc.
Reply by ●January 26, 20062006-01-26
VSP wrote:> > Could you or anyone else atleast tell me a good online source where i can > read about how the FAX data to be transmitted is exactly coded. > > Again, i am trying to look for a property in this coding that would help > me distinguish it from other transmissions eg some kind of periodicity in > the coded signal etc. >You do not need to know how the fax works to distinguish the fax/modem transmission from the speech. The spectum of the speech rolls down toward the high frequency; the spectrum of the data transmission is basically flat. All you have to do is to weight the high frequencies vs low frequencies. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●January 26, 20062006-01-26
> > >VSP wrote: > > >> >> Could you or anyone else atleast tell me a good online source where ican>> read about how the FAX data to be transmitted is exactly coded. >> >> Again, i am trying to look for a property in this coding that wouldhelp>> me distinguish it from other transmissions eg some kind of periodicityin>> the coded signal etc. >> > >You do not need to know how the fax works to distinguish the fax/modem >transmission from the speech. The spectum of the speech rolls down >toward the high frequency; the spectrum of the data transmission is >basically flat. All you have to do is to weight the high frequencies vs >low frequencies. > >Vladimir Vassilevsky > >DSP and Mixed Signal Design Consultant > >http://www.abvolt.com > >hi I can a novice in DSP so. please help me out a little more. Can the fact that the spectrum of speech rolls down towards high frequency be used to distinguish it other data transmission as well. That is to say, is this property unique to speech only?
Reply by ●January 27, 20062006-01-27
Yes, The fax machine originating a call sends a series of 0.5s tones with gaps of 3s between them at 1100Hz at the start of the call. The fax machine receiving a call sends a 2100Hz tone shortly after it answers the incoming call. This is often used to switch off echo cancellers along the route. You may need to look for both tones as under some circumstances one or the other is not sent. See ITU-T T.30 John
