Audacity Forum

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?

Koz

Hi Koz,

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?

armeniki wrote:I did want to know if there's a plugin which removes certain Frequencies which are below a certain dB... does that exist?

Steve made an Ultra-narrow filter plug-in which can be downloaded here … http://forum.audacityteam.org/viewtopic ... 073#p78073

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.

if it is just dial tone to indicate off hook
you can use any freq you want

it only plays in the handset to the user

so
buy a ma bell type IC, or dupe ma bell tone freqs for replay,
or make up your own freq for dial tone

buy a tone here
(0:30) TELEPHONE DIAL TONE SOUND: A clear, continual dial tone followed by 'hang up' beeps - delivered in CD quality WAV format http://www.tradebit.com/filedetail.php/ ... fect-1-wav

if it is truly dial tone all you need is for the user to hear it

use 450 alone like the majority of countries

or 425 alone like many countries
Most of Europe uses a single dial tone of 425 Hz.
http://www.wisegeek.com/what-is-a-dial-tone.htm

or use 350 alone like in the UK etc

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

you are getting hung up on a non problem

maybe your tones are not stable
http://en.wikipedia.org/wiki/Dual-tone_ ... requencies

maybe the hardware has nonlinearity problems
since you cant change that
you willhave to use a single tone

armeniki wrote:...
I did want to know if there's a plugin which removes certain Frequencies which are below a certain dB... does that exist?

a limiter would eliminate all that other crud in the picture way above
and leave you with two (perhaps jittery or at least wide) freq tones.

if it isnt the audacity instrumentation then your tones do not look pure to me. how solid is your source ?

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.

Koz

kozikowski wrote: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.

The tones in the "system_dialtone" example are actually closer to 440 and 352 Hz, whereas the "regular_350+440" sample is dead on 440 and 350.