Hi - I am trying to convert audio recording that was previously recorded from 16000 Hz to 8000 Hz. I’d like to change this without changing the audio drastically.
I need the recording to be saved as (which is compatible with Five9 software):
WAVE audio
ITU G.711 mu-law
mono 8000 Hz
Typically, I can change the Hz in the bottom left corner, but in recent weeks that hasn’t worked for me with without drastically changing how the audio sounds.
Thanks in advance for any help or tips you have!
in recent weeks that hasn’t worked for me
It should have worked for you never. 16000 sample rate supports sound quality between AM and FM radio. 8000 quality is just a bit better than a telephone.
You can make it worse or play other tricks. For example, if the original work was already damaged (muffled) and then upsampled to 16000, downsampling to 8000 later will appear to make no difference. The work is already fuzzy.
Koz
Typically, I can change the Hz in the bottom left corner, but in recent weeks that hasn’t worked for me with without drastically changing how the audio sounds.
You’re going to lose the higher frequencies and there’s no getting around that. The G.711 (8-Bit ADPCM) is going to add some “damage” too, assuming you’re starting-out at 16-bits.
The Nyquist theory says your audio can’t go above half the sample rate. (You need to sample the top-half of the wave at least once per cycle and the bottom-half at least once per cycle.) That means with an 8kHz sample rate your audio can’t go above 4kHz.
With music you’ll mostly notice that cymbals sound dull and with voice the “T” and “S” sounds will sound dull (or muffled). The “traditional” human hearing range is 20Hz to 20kHz (for a young person with normal hearing) so the CD sample rate is set at 44.1kHz to cover the full range (and to allow for imperfect filtering).
4kHz is considered the minimum for good intelligibility so to get maximum utilization of bandwidth the phone company limits the voice bandwidth to 4kHz (8000Hz sample rate).
If you want to get an idea of how this filtering affects the sound, you can experiment with the Equalization effect. (For experimenting, i recommend the Graphic EQ mode with the Preview option.) The lower frequencies are on the left and the higher frequencies are on the right, so pull-down the sliders on the right to see how filtering-out the highs affects the sound.
While you’re at it with Equalization, try boosting the 2kHz - 4kHz range to see if you can partially make-up for the lost higher frequencies.