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Spectral Frequency Question

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Matthew Chung
Spectral Frequency Question
on May 3, 2013 at 8:08:49 pm

I have several voice recordings that I am encoding to mp3 to stream at 16kbps. I was given a sample wav file which encodes to 16kbps mp3 fine and which encodes with a lot of sound artifacts. (wav files below)

(wav file that encodes fine)

(wav file that does not encode well)

When looking at the spectral frequency display of the two files, the one that encodes fine has a frequency under 4k and the one that does not has a frequency over 10k (images below)

(encodes fine frequency)
(encodes not so good frequency)

I believe I understand why the second file encodes to mp3 with artifacts, because of the high frequency, but what I do not understand is why the second file has such a high frequency. I believe the human voice has a frequency of 300hz to 3400hz ( so how is it possible that it has a frequency over 10k?

Also, if the frequency is why the encoding is introducing artifacts, is there a way to record audio such that it is within a certain frequency?

Thanks in advance

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Angelo Lorenzo
Re: Spectral Frequency Question
on May 4, 2013 at 7:56:00 pm

The human voice is rich in harmonics and overtones. Anything past 5-6K is considered "air" or "lightness" in terms of adding to the human voice.

To remove it before compression use a low pass filter effect. MP3 encoders usually incorporate a low pass filter, but they're rarely as good as doing it yourself before compression.

Angelo Lorenzo

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