What audio file types are supported?
Our DTMF Detection is known to work with the following
- 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.
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" 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
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.
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.
If you have any questions regarding our online DTMF detection
tool that are not answered here, please send us email.