Digital audio from a sound card

In summary, the process of audio programming involves sampling a time domain signal, storing the samples, and reconstructing the audio wave in the time domain by using the samples to represent a voltage at discrete time intervals. The use of the FFT may also be involved in compressing and decompressing audio, but the basic process remains the same. The sound card has a digital to analog converter and outputs the signal at the same rate as it was sampled, representing the instantaneous amplitude of the original sound. The output is then filtered and presented to an audio amplifier.
  • #1
FrankJ777
140
6
I would like to do some audio programming for a school project, but I'm not sure how a computer processes audio and reconstructs it in a sound card. I've had a signal processing course that covered standard DSP topics but I'm not sure when or how they are applied to acquire, store, and reproduce audio through a sound card. In trying to find a functional explanation I usually see it explained as sampling a time domain signal, storing the samples, and then reproducing audio wave in the time domain by using the sample to represent a voltage at discrete time intervals. But use of the FFT is always mentioned, but I'm not sure how it all fits together. So I have two "theories" about how it's accomplished.

a) A audio signal x(t) is sampled, which represents signal voltage levels at discrete time intervals x[n]. The time domain samples are stored in memory. Then the time domain samples are used to output a voltage signal by setting a voltage level to the value of the sample x[n] at time intervals of the sampling period.

b) A audio signal x(t) is sampled as before. The samples x[n] are then passed to an FFT then the frequency domain values X[k] are stored in memory. Reconstruction is accomplished by oscillators in the sound card which each oscillate at a discrete frequency (for time intervals of the sampling period) at the magnitude indicated by the value of the sample X[k].

Or, in other words. When you give data to a sound card to output audio, is your data a time domain representation of the signal where each successive data value represents the magnitude of the wave at a time interval x[n], or does the data you give sound card represent discrete frequency values X[k] at time intervals.

I know this question is verbose, but I think the easiest way for me to gain understanding is to explain what I think is going on as I understand, and let somebody else tell me where I'm looking at this wrong. I hope someone can straighten me out on this.

Thanks.
 
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  • #2
The typical setup is a). During the conversion from digital back to analog (D/A), you will also need some sort of filter to smooth out the steps in your output which occur at the sampling/reconstruction frequency.

If lossy audio (or video) compression are performed, an FFT (or a subset, usually) is performed on the sampled stream and then appropriate processing is performed. Decompression requires the inverse FFT and then you do the same D/A conversion as before.
 
  • #3
Or, in other words. When you give data to a sound card to output audio, is your data a time domain representation of the signal where each successive data value represents the magnitude of the wave at a time interval x[n], or does the data you give sound card represent discrete frequency values X[k] at time intervals.

The sound card has a digital to analog converter in it and the outputs are generated at the same rate as they were sampled.
The outputs represent the instantaneous amplitude of the original sound and, after some filtering to get rid of components above human hearing, the result is presented to an audio amplifier.
 

What is a sound card?

A sound card is a hardware component in a computer that allows for the input and output of audio signals. It is responsible for converting digital audio signals into analog signals that can be heard through speakers or headphones, and vice versa.

How does digital audio from a sound card work?

The sound card receives digital audio data from the computer's processor and converts it into analog signals. These analog signals are then amplified and transmitted to speakers or headphones, where they are converted back into sound waves that can be heard by the user.

What are the benefits of using a sound card for digital audio?

A sound card can provide high-quality audio output, with better sound fidelity and a wider range of frequencies compared to the built-in audio capabilities of a computer. It also allows for more precise control over sound settings and can support multiple audio channels for surround sound.

How can I improve the performance of my sound card for digital audio?

To improve sound card performance, make sure to install the latest drivers and software updates. You can also upgrade to a higher-quality sound card with better components and features. Additionally, optimizing your computer's overall performance can also help improve the performance of your sound card.

Can I use a sound card for recording audio?

Yes, sound cards can also be used for recording audio. Many sound cards come with built-in input ports for connecting microphones or other audio recording devices. They also often have software for recording and editing audio, making them a useful tool for musicians, podcasters, and other content creators.

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