The blog post explores the physics behind the distinctive "whoosh" sound created by passing objects like airplanes. It explains how this sound isn't simply the object's engine noise, but rather the Doppler-shifted frequencies of ambient noise—like wind, traffic, or conversations—being compressed as the object approaches and stretched as it recedes. This effect, similar to how a siren's pitch changes as it passes by, is most noticeable with fast-moving objects in relatively quiet environments. The post further delves into how our brains perceive these shifting frequencies, potentially misinterpreting them as the sound of the object itself and sometimes even creating phantom whooshing sensations when no physical source exists.
The author investigates strange, rhythmic noises emanating from a US Robotics Courier V.Everything 1670 external modem. Initially suspecting a failing capacitor, they systematically eliminated various hardware components as the source, including the power supply, cable, and phone line. Ultimately, the culprit turned out to be a loose metal plate inside the modem vibrating against the plastic casing at specific frequencies, likely due to the interplay of electrical signals and component vibrations within the device. Tightening the screws securing the plate resolved the issue. The author reflects on the challenge of diagnosing such elusive hardware problems and the satisfaction of finally pinning down the root cause.
HN commenters discuss the nostalgic appeal of the 1670 modem's sounds, with some sharing memories of troubleshooting connection problems based on the audio cues. Several delve into the technical aspects, explaining the meaning of the different handshake sounds, the negotiation process between modems, and the reasons behind the specific frequencies used. The infamous "Concord jet taking off" sound is mentioned, along with explanations for its occurrence. A few lament the loss of this auditory experience in the age of silent, high-speed internet, while others express relief at its demise. There's also discussion of specific modem brands and their characteristic sound profiles, alongside some speculation about the article author's connection issues.
Surface-Stable Fractal Dithering introduces a novel dithering technique that maintains detail and avoids shimmering artifacts when applied to animated or deforming 3D surfaces. It achieves this by generating spatially correlated dither patterns using fractal Brownian motion, ensuring temporal coherence as the surface changes. This method produces visually pleasing results for various applications like reducing banding in low-bit color displays or adding stylized noise to textures, outperforming traditional dithering approaches in dynamic scenarios. The provided code implementation offers a flexible and efficient way to integrate this technique into existing graphics pipelines.
Hacker News commenters generally praised the visual appeal and technical ingenuity of the dithering technique. Several highlighted the cleverness of leveraging 3D surfaces for dithering, finding it both unexpected and effective. Some expressed curiosity about the performance and potential applications, particularly in real-time scenarios and stylized rendering. A few commenters delved into the technical details, discussing the specifics of fractal noise generation and the implications of different surface types. There was also a brief discussion comparing this method to traditional dithering techniques and its potential advantages in preserving detail and minimizing banding artifacts. One commenter suggested potential improvements like exploring alternative distance functions and optimizing for different color spaces.
Summary of Comments ( 32 )
https://news.ycombinator.com/item?id=43713524
Hacker News users discuss various aspects of the "whoosh" sound phenomenon. Several commenters offer additional examples of sounds exhibiting similar characteristics, such as the Doppler shift observed with passing cars or the sound of a large truck passing a house. Some discuss the physics behind the phenomenon, including the role of air pressure changes and the shape of the object creating the sound. Others delve into the subjective experience of these sounds, noting how perception can be influenced by factors like background noise and individual sensitivity. One compelling comment highlights the prevalence of this effect in movies and its potential exaggeration for dramatic effect. Another interesting observation is the comparison to the "sonic boom" of a supersonic aircraft, contrasting the continuous whoosh with the sharp crack of the boom. Finally, a few commenters mention the psychological impact of these sounds, including their potential to be unsettling or even anxiety-inducing.
The Hacker News post titled "Passing planes and other whoosh sounds," linking to an article on windytan.com about the physics of whooshing sounds, has generated a modest discussion with several interesting comments.
One commenter shares a personal anecdote about experiencing the Doppler effect with the sound of a passing plane, noting the distinct drop in pitch as the plane moves away. They also connect this experience to the sound of cars passing by, highlighting the commonality of the phenomenon in everyday life.
Another commenter delves into the specifics of the Doppler effect, explaining how the frequency shift is dependent on the relative velocity between the source and the observer. They then raise the question of why the sound of a passing plane seems to "whoosh" down rather than up, even though both rising and falling frequencies are involved. They hypothesize that this perceived downward shift is due to the greater change in frequency occurring as the plane moves away, alongside the general decrease in loudness as the source recedes.
A subsequent comment builds on this hypothesis, suggesting that the human ear is more sensitive to downward frequency changes and that the decreasing volume of the receding sound source might contribute to the perception of a downward whoosh.
Another commenter links to a Wikipedia page about the sonic boom, a different phenomenon associated with supersonic aircraft, distinguishing it from the Doppler effect discussed in the original article. This comment helps clarify the different types of sounds generated by moving aircraft and their underlying physical principles.
One user mentions their experience with sailplanes, explaining how the quiet nature of these aircraft allows for a clearer perception of the Doppler shift and a more pronounced "whoosh." This adds another real-world example to the discussion and highlights how the surrounding environment can influence the perception of these sounds.
Finally, a commenter with a background in audio engineering provides a more technical explanation, mentioning how the perceived pitch of complex sounds like those produced by aircraft engines is not solely determined by the fundamental frequency but also influenced by overtones and harmonics. They suggest that the Doppler effect's influence on these different frequency components might contribute to the complex nature of the perceived "whoosh."
In summary, the comments on the Hacker News post provide a range of perspectives on the physics and perception of whooshing sounds, from personal anecdotes to detailed explanations and related phenomena, demonstrating a shared curiosity about the acoustic world around us.