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DTMF-Detect Frequently Asked Questions

General Questions

What audio file types are supported?

Our DTMF Detection is known to work with the following file types:

  • Sun/NeXT audio data (u-law, a-law, or PCM)
  • Microsoft RIFF, WAVE audio data

These formats are supported at 8 and 16 bits, mono and stereo. Other formats such as ADPCM, IMA_ADPCM, SMP, IRCAM, SoundTool, VOC, HCOM, AIFF, or SPHERE, may also work, but your mileage will vary. The safe thing to do is to convert the sample into a mono 16,000Hz .wav or .au before running it through our DTMF detection tool.

What is the maximum sample size?

Our tool will not deal with samples over 20 seconds in length. You should clip your audio sample so that only contains the DTMF tones.

What about background noise or other noises in the sample?

Our tool is pretty good about picking out the DTMF tones even if there are other noises such as white noise, music, speech, or even dial tones.

What if I recorded the DTMF tones on an analog tape recorder which is slightly fast or slow?

No problem. Your recording can be as much as 10% too slow or fast. As long as you make sure that your sample only (or mainly) contains the DTMF tones, the tool will calibrate itself to find the recording speed.

What about volume?

If you can play the sample on your computer and clearly hear the DTMF tones, our tool should be able to detect them.

I clipped the audio sample and coverted it to one of the recommended formats and I still get error messages when I submit the audio sample file.

Email the audio sample to us and we will try to help.

My WebTV wont let me upload sounds

That is correct. You will need to use a real computer in order to do this.

Report Format

Sample Format

The "sample format" indicates the type of audio sample received from you. Our software runs through a number of tests examining both the file type, the MIME data type suggested by your web browser, as well as the raw data itself in order to determine the audio encoding used, its sample rate, and the number of channels.

Sample Size

"Sample size" shows the number of bytes in the audio data, the number of samples, and its approximate length (in seconds). The number of "usable samples" indicates how many samples were used for the DTMF detection. The remaing samples at the end of the clip -- usually no more than 20milliseconds -- are discarded because of the way the tool slices up the sample at the beginning of the analysis.

DTMF Base Frequency

The DTMF detection tool cailbrates itself to your recording in case the sample was taken from an analog recording device. The DTMF Base Frequency is the lowest of the eight DTMF frequencies an should be 697 Hz, but may be slighlty different depending on your sample. This may be because your sample is slightly slow or fast, because the DTMF tone was slightly off, because the recording device was not stationary with respect to the phone, but most likely because of limitations inherent in signal analysis and an in our own software.

Tones Found

This section lists the tones found in the audio clip. The star times and lengths should be consistent with what you see in the graphic above the table. Because of the way our tool works, the start and end times for the DTMF tones are not precisely known, but should be within the given interval.

Ask Questions

If you have any questions regarding our online DTMF detection tool that are not answered here, please send us email.

Last updated Tuesday December 11 2012
For more info contact Zeebar Technology Services, Inc..
(C) Copyright 1996-2006 by Helmut Hissen and Zeebar Technology Services, Inc.
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Zeebar Technology Services, Inc