Video lectures about audio measurements, audio myths, PCM encoding
By learning some audio engineering concepts we can avoid typical stereotypes and marketing lies. Anyone who is interested in audio reproduction should watch these videos at least once in their lifetime.
Ethan Winer - Audio Myths Workshop
Purpose of this video is to identify what really matters in audio reproduction and what does not. The presentation walks through different topics:
- Auditory memory (why blind and controlled tests are important).
- Proper test methods (understand what is and what is not a valid test).
- Why some people still believe in audio magic (unreliable auditory memory, confirmation bias, room reflections).
- How audio fidelity is measured. The four audio parameters.
- Artifact audibility.
- Alternative test methods: nulltest, 'converter loop-back'.
Ethan Winer is a former audio engineer, computer programmer, technical writer and 'infamous' audio mythbuster. He has published several articles in audio and computer magazines.
Digital Show & Tell (Monty Montgomery @ xiph.org)
There is a huge amount of misinformation on the net about how digital audio works. The behavior of digital signals is counterintuitive, and if something is counterintuitive than stereotypes, false beliefs easily fill the gaps and replace the real explanations. Nowadays high resolution music services and high resolution audio hardware vendors use these stereotypes as a 'marketing tool'. Some misconceptions about digital audio:
- "Digital audio is inferior to analog."
- "The time resolution of pulse-code modulation (PCM) is the sampling period."
- "Higher sampling rate offers higher resolution in time." (false conclusion of the above misconception)
- "Sampling theory only applies to sine waves."
- "Sampling theory is only a theory." (WTF. What does that mean?)
- "Increasing the bit-depth increases accuracy or resolution." ('Resolution' is an incorrect term in digital audio. There is no such thing as 'resolution', only bit-depth and noise level.)
- "Digital can't represent analog values below the least significant bit."
In the following 20 minute video Christopher "Monty" Montgomery dispels the false beliefs and corrects many misconceptions about digital audio (pulse-code modulation or PCM). The video is easy to understand and sampling, quantization (bit-depth) and dither is demonstrated with real instruments. The point is that the output of a properly dithered and filtered digital system is indistinguishable from a band-limited pure analog system with the same noise floor. Digital systems are free from timing errors and modern oversampling DACs (digital to analog converters) have no stairsteps in their waveform.
The article mentioned in the video (24/192 Music Downloads ...and why they make no sense) is still available in the Wayback Machine here.
Christopher "Monty" Montgomery is the creator of the Ogg container format and the Vorbis audio codec, and the founder of The Xiph.Org Foundation. FLAC and Opus audio codec were also developed at Xiph.Org. Opus is an official web standard and the most widespread audio codec on YouTube. (note: the speech codec for Opus was developed at Skype, the general purpose codec was developed at Xiph.)
Floyd Toole - Sound reproduction – art and science
No single 'curve' or measurement can describe the sound of a loudspeaker, because we listen in reflective spaces. In a typical room the on-axis response makes only a small contribution to the total sound and the contribution of early and late reflections to the in-room response is not negligible. There is a strong correlation between the off-axis performance of loudspeakers and how these early and late reflections affect the in room response.
The video is a brief summary of Dr. Toole’s research on loudspeaker measurements and human perception.