Voice Prompt Recording
To record high quality voice prompts for your
voice mail or interactive voice response (IVR) system, you should not
use the telephone handset microphone. The handset microphone is by far
less sensitive than even a cheap studio microphone, and has dynamic
range that is not enough for a quality narration.
Every type of microphone is different. You
will need a studio microphone designed specifically to record voice.
These microphones have a specific dynamic range to only record
frequencies, and cut off all other frequencies (e.g. low-frequency
Do not use the microphone supplied with your
sound card, they are usually on the lower end of quality. There are a
number of microphones available that were designed specifically for
sound card use.
On the higher end there are high-quality
studio microphones. Most high quality microphones, however, cannot be
connected directly to the sound card. They must be connected first to
a separate microphone 'preamplifier' ("preamp") that is connected to
the 'Line Input' of your sound card. With this setup the recording
sound quality will be greatly improved.
The microphone you use should be "unidirectional"
(picks up sound in a single direction). "Omnidirectional" microphones
pick up sounds from all directions, resulting in all noise in the room
being recorded along with the voice.
Most microphone preamplifiers built into sound
cards are of poor quality. As a result, recording the sound through
the Line input, instead of the Mic input, may also improve the
Make sure you don't move the microphone around
as this will create microphone handling noise on your recording. Using
a microphone stand is a good idea; you can simply place a microphone
on a pile of books if you don't have a microphone stand.
Place the microphone in about 15 - 30 cm (0.5
- 1 ft) from your mouth when recording (of course, the mic must be
sensitive enough to support this distance. If the mic is closer than
1/2 ft, it will most probably record bubbling and other unpleasant
Recording sound quality varies greatly on
different sound cards, especially the
noise level of the sound cards.
Most modern sound cards report a respectable SNR (signal to noise
ratio, the measure of noise added by the card). In reality, the noise
level is often higher than the specifications because of the
interference between the electrical components inside your computer.
This causes the recording to have more background noise, especially
when recording using the built-in microphone input.
To improve the SNR of your recordings, avoid
using sound cards that are built into the motherboard (usually called
'integrated sound card'). Get a good card in a price range of $50-100
You may use any of the available sound editing
applications. Avoid using MS Sound Recorded that comes with Windows;
its implementation of downsampling provides unacceptable sound
These tools provide both quality and powerful mixing and audio
When you initially record the voice prompts,
use the highest available recording format. 44100 Hz, 16-bit, mono is
recommended. Only downsample the recording sound when you are surely
done with the processing and mixing.
Make sure to save your original voice prompt
before starting editing the file.
If you want to filter out noise, equalize, add
some music background or audio effects to your voice prompts, do it
now. The number of tools and effects available depends on the software
you used to record the voice prompt.
As a final stage of recording your voice
prompts, you will need to downsample and save the recording to a
format supported by telephony hardware. The final audio format depends
on the telephony hardware you use. Dialogic cards (www.dialogic.com)
require 11 kHz sound; all other telephony devices, including
modems and other telephony boards, such as
require 8000 Hz, 16-bit, mono format.
- Pick the best unidirectional microphone
allowed by your budget
- Position and properly fix the microphone
- Set the level of recording
- Select software you are going to use for
- Select best available recording format
(44100 PCM / 16 bit / mono)
- Record your voice prompts
- Save the original, uncompressed PCM WAV
- Only do sound post-processing, mixing,
equalizing and noise filtering with a copy of the file
- After you are done with the post-processing
and audio mixing, re-sample the file to the quality appropriate for
telephony (11025 Hz for Dialogic, 8000 Hz for all other cards;
16-bit PCM is recommended)
- Save the resulting file in a supported
format (11 kHz or 8 kHz, 16 bit, mono).
If you prefer your IVR voice prompts recorded professionally in the
studio, please contact us for
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