I have some audio files that are supposed to be 24bit 96k (according to the metadata/media info). When I open them in Audacity the project rate changes to 96000, but when I view them in Spectogram they peak around 48k, and if I analyze with the Plot Spectrum tool it shows the same thing. What gives, am I missing something?
Nyquist theory…
96kHz is the sample rate. If you don’t know what that is, take a look at [u]this page[/u]. The spectrogram shows the audio content.
You need at least 2 samples per cycle (one data-point for the positive half of the cycle, and one data-point for the negative half). At a sample rate of 96kHz, your “audio” can’t go above 48kHz. (It’s not really audio above the audible hearing range.)
It’s good to know that Audacity famously doesn’t have Clip INFO. That’s why you need to either do it second hand, or use an external program.
The audio tools are measuring audio. The highest sound that 96000 sample rate will manage is half. That would be 48000 Hz audio.
Remembering that actual audio doesn’t go much higher than 20000Hz, so are we doing this for a specific reason, or the files were delivered that way and that’s the way it is? Those two sound file specs are typical of a studio recording.
Koz
The maximum audio frequency is half the sample rate (known as the “Nyquist frequency”).
To handle the full audio range (up to 20 kHz / 20,000 Hz), the sample rate must be at least 40 kHz (40,000 Hz). In practice, the sample rate needs to be a little higher, which is why the sample rate for CDs is 44100 Hz (44.1 kHz).
Ahh…thanks a million guys, very helpful info.