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  • Blog Post: You can't hear DC

    Recently one of my team members found a bug in some old code while doing a code review. Our application was generating a sine wave to be rendered by the audio hardware. The sample format isn't important except to note that it is an unsigned value between 0 and MAX = 2*FS_AMP. The bug is in the following...
  • Blog Post: More posts eventually!

    It's that time of year, it seems. I was down with the flu last week, and I'm trying desperately to catch up this week. I promise I'll get more posts up soon. I'm doing some WASAPI playback library stuff right now and I'm just dying to do a couple of articles about the new Vista audio APIs. I'm...
  • Blog Post: Digital Audio: Aliasing

    Sampling a continuous waveform into discrete digital samples results in lost information. Discrete samples can only tell what the wave is doing at periodic instants in time, and not what's happening between them. The continuous sampled wave could be doing anything between samples. We simply don't know...
  • Blog Post: Clipping in popular music

    Aside from the distortion artifacts, one of the biggest problems that results from clipping is a loss of dynamic range. Remember that the dynamic range of a signal is effectively the difference between the maximum output level and the noise floor . When you clip a waveform, you lower the maximum sample...
  • Blog Post: Louder Sounds Better

    Below is an example of the Fletcher-Munson Equal Loudness Curve . It is one of the most recognized graphics in audio engineering. The horizontal axis is frequency of tones, and the vertical axis is actual sound pressure in dBSPL. Each point on a curve has about the same subjective "loudness" to the human...
  • Blog Post: Audio Fidelity: Clipping

    In theory, an audio signal can take on any amplitude. There is no mathematical upper limit for how far from zero a sample can go, or how high the magnitude of a continuous wave can go. In practice, however, a digital signal's amplitude is limited by its number of bits, and even electrical components...
  • Blog Post: The difference between measuring DR and THD+N

    I've talked here before about how noise and distortion are very similar concepts with very different causes. Noise is unwanted artifacts independent of the signal often caused by physical processes outside of a device. Distortion is unwanted artifacts directly correlated with the signal usually caused...
  • Blog Post: Audio Fidelity: Output Level

    Output level is one of the simplest fidelity metrics to understand, but don't take that to mean it's not important. There are several occasions where you want to know the maximum, loudest value that a signal can get. On the digital side, that's pretty easy. A full-scale digital signal is a waveform ...
  • Blog Post: Always dither before you quantize

    Quantization adds noise. Taking a nice continuous signal and expressing it as distinct integers will introduce a round-off error, which means you've added random fluctuations to the signal, which is the definiton of noise. Remember that noise is inevitable , so we just have to manage it (such as using...
  • Blog Post: Audio Fidelity: Frequency Response

    Not all frequencies are created equal. And they're also not generally treated equally by a digital filter. How inequally they're treated is one of the defining characteristics of a filter. Audio engineers have a metric for describing this behavior. The frequency response of a filter or system tells us...
  • Blog Post: Audio Fidelity: Crosstalk

    For years, recorded audio was just a signal, captured by a microphone, stored as an audio signal, and then played back by a speaker. The microphone acted as a "proxy" eardrum to hear the sounds when and where the real listener's ear couldn't be. But somebody made an important realization. Most people...
  • Blog Post: 32 bit audio redux

    In my previous post , I don't think I explained very well why a 32-bit signal wouldn't work on the low-end. The point, I think, was well-taken on the high-end. You don't want a 192 dBSPL audio signal applied to your body (or your planet, for that matter). However, Tricky asks Why have the 6.02 dB increment...
  • Blog Post: A Lesson in Dynamic Range (or Why 32 Bits per Sample Should Never Catch On)

    Anywhere you go, you will be able to find people who will insist that more is better. Bigger cars, larger portions, and more bits in your audio samples. But we thinking people know that there is such as too much of a good thing, don't we? I refer, of course, to having too many audio sample bits. The...
  • Blog Post: Quantization, Sample Rate, and Bits Per Sample

    Forgive my digression, but I need to lay some digital signal processing ( DSP ) groundwork for what I want to talk about next. If you're already a DSP guru, then you may want to skip this one. (If you're a DSP guru, what're you reading a blog called "Audio Fool" for anyway?) As you know, a physical audio...
  • Blog Post: Audio Fidelity: Distortion

    Distortion in audio is very closely related to noise. Both "distortion" and "noise" are used to describe unwanted components of an audio stream, so what's the difference? I already defined noise when I talked about dynamic range . But what is distortion? The simplest answer is that distortion is signal...
  • Blog Post: Why is everything in audio measured in dB?

    Short answer: Because the ear measures things in dB. The decibel is nothing more than a ratio between two numbers. (The unit was originally just a bel, but for audio it was more convenient to use tenths of a bel, hence the SI 'deci' prefix) Mathematically, the number of decibels between two numbers is...
  • Blog Post: Audio Fidelity: Dynamic Range

    I want to talk about noise for a minute. We all know what noise is, and that we don't want it in our audio. Unfortunately, noise is always present, whether we want it or not. In pseudo-technical terms, noise is random unstructured variations in a signal. In a digital signal, that variation comes from...
  • Blog Post: What's all this 'fidelity' stuff about anyway?

    Nearly everybody has heard the term "high fidelity". Most understand that fidelity is a desirable thing to have, and many believe that the word 'fidelity' is synonymous with 'quality'. In any casual (non-technical) setting, they are the same. But what does an audio engineer mean when he speaks about...
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