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> You need at least 2 samples to make an audible frequency. That's not strictly true. An audio file with a single non-zero sample (usually set to full amplitud

> You need at least 2 samples to make an audible frequency. That's not strictly true. An audio file with a single non-zero sample (usually set to full amplitude) is often used for testing -- usually called a Dirac impulse or similar. That impulse will be (necessarily) band-passed by the playback hardware and put out filtered "white" noise. That impulse can be recovered by a mic to show e.g., pre-ringing caused by (FIR) filters. An FFT of that impulse will show the playback hardware's response in the frequency domain vs full bandwidth. > Thinking of the sample rate as a 'set frequency' For e.g., a WAV file, that's a fixed number of samples per second (a frame being 1 sample x n channels). That is a set frequency, and deviating from it will alter the pitch of the music. There really is no case where sample rate varies, unless we're talking about minute variations between the clock signals of different hardware, which requires the use of sample rate conversion to match. A related concept is the bits-per-second of lossy formats (e.g., AAC) which may vary from frame to frame (and that frame will mean something different from a WAV frame). > You need at least 2 samples to make an audible frequency. I think you're confusing this with Nyquist being 1/2 of the sampling frequency. You can very much capture an audible signal with a single sample, but that signal will be limited (by hardware, by Nyquist, etc). [Edit] I should say that this single sample has to be non-zero and the playback system has to have a DC-offset that isn't equal to that sample's amplitude.

taneq 7y ago
> That's not strictly true. An audio file with a single non-zero sample (usually set to full amplitude) is often used for testing -- usually called a Dirac impulse or similar. Is this a PCM type sample or a frequency-domain sample? If the former, how frequently does this impulse get repeated in order to turn into white noise after going through the playback hardware? It sounds like if it's not repeated it should just make a nasty 'pop'. > I should say that this single sample has to be non-zero and the playback system has to have a DC-offset that isn't equal to that sample's amplitude. As I understand it, if you try to play a PCM audio file with a uniform value, you're effectively putting DC through the speakers, driving them to a particular offset where they'll stay until the end of the track. Is that not the case?
munificent 7y ago
I don't think your comment is in conflict with the parent comment. Yes, a single sample file can produce a sound — a tiny impulse spike "tick" — but that sound doesn't have any audible frequency or pitch because there's no oscillation or tone.
anon9001 7y ago
This is more correct than how I think about it :) > You can very much capture an audible signal with a single sample, but that signal will be limited (by hardware, by Nyquist, etc). This makes no sense to me, but it's obviously true because this exists: https://en.wikipedia.org/wiki/1-bit_DAC https://en.wikipedia.org/wiki/1-bit_DAC

taneq 7y ago

> That's not strictly true. An audio file with a single non-zero sample (usually set to full amplitude) is often used for testing -- usually called a Dirac impulse or similar. Is this a PCM type sample or a frequency-domain sample? If the former, how frequently does this impulse get repeated in order to turn into white noise after going through the playback hardware? It sounds like if it's not repeated it should just make a nasty 'pop'. > I should say that this single sample has to be non-zero and the playback system has to have a DC-offset that isn't equal to that sample's amplitude. As I understand it, if you try to play a PCM audio file with a uniform value, you're effectively putting DC through the speakers, driving them to a particular offset where they'll stay until the end of the track. Is that not the case?

munificent 7y ago

I don't think your comment is in conflict with the parent comment. Yes, a single sample file can produce a sound — a tiny impulse spike "tick" — but that sound doesn't have any audible frequency or pitch because there's no oscillation or tone.

anon9001 7y ago

This is more correct than how I think about it :) > You can very much capture an audible signal with a single sample, but that signal will be limited (by hardware, by Nyquist, etc). This makes no sense to me, but it's obviously true because this exists: https://en.wikipedia.org/wiki/1-bit_DAC https://en.wikipedia.org/wiki/1-bit_DAC