I’m just about going to pull my hair out (well not really but am close to it!)
We’re working on a telecom project and I’ve come accross really strange results when using two different files for dial tone audio.
When we upload a plain .wav file with the two tones required for dial tone (350 and 440) as a sine wave, it plays but has a warbling affect in the background… this may be because of the equipment itself and we’ve come to the conclusion that we cannot change it.
However, oddly enough, when we upload a square wave file, it plays perfectly… the only problem though is that using a square wave 350+440 tone generates a lot of other noises (high pitched)… when we try and use the equalizer to cut down the other freqs, it does it but it basically changes the square wave to a sine wave and we’re back to the same result.
I have played around with the actual waves and used the pencil tool to re-draw “modified sine waves” which helps but as I’m not a computer, I do make mistakes when I redraw them and the sound comes back a bit off… so we’ve concluded that the equipment is better able to handle square wavish files.
So my question is if there’s a plugin which can convert a square wave into a modifed sine wave? (see the attached pic I found on the net if that helps).
I’ve also attached a couple of files to give you an idea of the differnce… one is the “system recording” which is an audio recording from another working system’s dial tone… if you run it through the frequency analysis you can see there are heaps of other freqs in there… there’s a slight tone to it… and the other is just a plain 350+440. I know the difference is barely noticeable…
I know this may not make a lot of sense but let me know and I’ll clarify any questions you may have.
I’m not quite sure what you are after.
Do you want band limited square waves in which the frequency band is limited to almost the fundamental frequency, so that it is almost a sine wave?
or do you want a low bit depth approximation of a sine wave?
or do you want something else?
I’m afraid the warbling is not quite apparent except for when it’s on the system we’re using…
but I think your suggestion of a band-limited sqaure wave is an idea.
The system_dialtone sample does look like a band-limited square wave file I guess since there are so many other frequencies in the analysis screen… and the square wave format would work perfectly with the equipment…
how do we go about doing that?
I also just thought of something… is there a way to cut off frequencies that are below a certain -dB? For example, in the freq analysis screen, I wanted to remove all freqs that were below -42dB?
quote:
However, oddly enough, when we upload a square wave file, it plays perfectly… the only problem though is that using a square wave 350+440 tone generates a lot of other noises (high pitched)… when we try and use the equalizer to cut down the other freqs, it does it but it basically changes the square wave to a sine wave and we’re back to the same result.
yup
basic law of the universe
low pass filter a square wave and you get sine wave(s)
see nyquist theorem;
and sample data system - data conversion ;
also fourier transform
Welcome to the design of Dial Tone Multi Frequency. The original tones were chosen so not only would the tones be unambiguous, but the harmonics and modulation products would not interfere with each other.
It’s more complicated than you think.
DTMF tones only sound correct on a system with no distortion. If you have a non-linear system or any system with significant distortion…
I’m afraid the warbling is not quite apparent except for when it’s on the system we’re using…
…like that one, you will get modulation products, beating, other tones, etc. The system was designed to survive this. Any good DTMF decoder will not care at all. Did you try actually decoding it, or did you stop designing when the tones didn’t sound right?
That’s basically what you have been doing with the Equalizer
Yes, if you look at the spectrum plot you could use a series of narrow band pass filters to allow the frequencies that you want, but I doubt that this will solve the problem.
If the sine tones are not working correctly, I think you need to look at why. Are you sure that the signal is at the correct level for the equipment?
Just a thought, if you have an old modem lying around, could you adapt that to generate the tones?
your problem is overconstrained
and has no solution
we can show you how to design a dtmf circuit that works
we can show you how to design hardware that works with dtmf
but nobody can force your mandated hardware to work with the mandated frequencies the way yuo say you have to do it
you can buy ma bell dtmf circuits
you can use your phone to record dtmf tones
but they may not be the freqs you want
but you should!!
those tones work without the intermodulation problems you have
tell us what you are working on so we can give you better alternatives
what you have is not going to work as you have found out
I know this may not make a lot of sense but let me know and I’ll clarify any questions you may have.
What’s the job? I mean the real job. We’re all floundering because nobody has The Big Picture. What do the tones do? What sort of telecom project is this?
Oh, so you’re not dealing with DTMF. This is really Dial Tone as in Off-Hook Notification Tone. Did you try recording one from someone with a land-line telephone? I may be able to do that for you. How long do you need it?
Yes, sorry I should have realised that there may not be other telecom people on this thread… yes, it is a Dial Tone (not DTMF - Dual-Tone-Multi-Freq aka Touch Tone).
Yes, that’s the issue I’m having as I do have a .wav file which I created but it’s not very clear… not sure if you saw the attachments to the posts I have already made (there are a couple of audio clips) the waveform needs to be a modified-sine or close to square wave… I tried generating the 350+440 Hz using square wave (even with no alias) and there is still a huge amount of other noises which I can’t figure out how to get rid of without using the Equaliser thing…
I did want to know if there’s a plugin which removes certain Frequencies which are below a certain dB… does that exist?
If you make two copies of your “system” dial tone (with the unwanted frequencies) , then apply Ultra-narrow @ 350Hz 5 iterations to one copy, then apply Ultra-narrow 440Hz 5 iterations to the other copy, and play the two filtered copies together, you get a dial tone which is even purer than the “regular” one you posted, A before-after example is attached ….
The phase between the 350 and 440 may be responsible for the modulation effect you are hearing,
If you apply ultra narrow filter to the two copies as I have described above, you can alter the phase by shifting the two filtered copies out of sync by a few samples.
do it like a cell phone - dont use any dial tone !
make it unique
Private or internal PBX or key phone systems also have their own dial tone,…sometimes different to remind users to dial a prefix for - or select in another way - an outside telephone line. http://en.wikipedia.org/wiki/Dial_tone#Variants
350/440. What happens when you use two tones that don’t have clear, unquestioned mathematical relationships to each other? That’s just asking for troubles. Throw either or both off frequency just a little and see what happens. This is a cousin to that suggestion of moving the phase around. Go further.
Are you in love with International Oboe A-440?
We had a thing going at NBC Television Network. New York Network Operations used 400Hz. Washington Transmission Center used International Oboe A-440Hz. It’s what passed for rampant individualism back east.
