there are differences between the frequencies of sounds, as 8000Hz , 16000Hz, 44100Hz , ....,etc.
why the researchers prefer the higher frequencies?
Hussein, not sure what you mean by " researchers prefer the higher frequencies". With respect to audio recording settings Stephen is definitely right, is this what you were interested in - i.e. why we record with higher sampling rates than one would think are necessary?
thanks for all.....
I mean , why we not record the sounds with unique sample rate?
Hi Hussein,
For music recordings on may apply 24bit, 96 kHz to be able to downsample after sound editing procedures for example. CD quality is 16bit 44.1 kHz since the early 80ies (Sony). One reason may be that human hearing roughly ranges between 20 and 20000 Hertz. Hence, 44.1 kHz is a logical sampling rate to capture the full (human) hearing range (Nyquist theorem). You can always use higher sampling rates and downsample afterwards. Just needs more storage. I think very generally the sampling rate should be determined by your research/engineering question.
Frequency approach to music, speech and hearing research has never ceased to raise fundamental questions since Ohm's Acoustical Law (1843) and Helmholtz's Resonance Theory (1877). Hussein's question above is just one of millions unanswered questions. . Stephen's reference above to the Nyquist theorem provides adequate answer to the question at hand. If I record musical instruments at say 8 k/Hz sample rate, the sound quality is relatively poor in comparison to the same signal recorded at a higher sample rate. In speech, you might find that different phonemes (particularly fricatives/sibilants) are not well captured at low sampling rates as you'll lose the high frequency components which are critical distinctive features (acoustically speaking). Thus, if you use a unique sample rate, you might limit yourself to a specific sound source. I adopt Xaver's procedure mentioned above. It is one wise way to discover what sample rate does to the quality of your recordings.
As Stephen has already said if you want to analyze sound segment which has some relevant data above 8 kHZ, you at least need sampling rate to be twice the maximum (16 kHZ or above), because of the Nyquist rate, which is the minimum sampling rate that satisfies the Nyquist sampling criterion for a given signal sound.
To answer your second question („… why we not record the sounds with unique sample rate?“). Higher sampling rate (44.1 kHz) needs more space on your hard disk (or other storage), but you can always, as Haver said, downsample signal afterwards. I also prefer simple procedure for recording, which leaves me more time to monitor other things (speaker rate, intensity etc.)
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