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大家好，我开发了一个名为 Outside In 的小型 iOS 应用（<a href="https://apps.apple.com/us/app/outside-in/id6759529344">https://apps.apple.com/us/app/outside-in/id6759529344</a>）。这个想法很简单：你可以把一部闲置或旧的 iPhone 放在户外（如门廊、窗台或后院），而将另一部放在床边。户外的手机会捕捉外面的声音——如蟋蟀、雨声、风声，偶尔还有猫头鹰的叫声——并通过本地 Wi-Fi 将这些声音传输到室内的手机上。你可以将室内手机翻面放下，伴着这些声音入睡。我之所以开发这个应用，是因为我和我的伴侣以前晚上会把窗户留一条缝，以便听到外面的声音，但外面的温度并不总是适合这样做。我希望能在不受天气影响的情况下，享受开窗时的声音。一些技术细节：这两部手机通过 Bonjour（NWListener/NWBrowser）相互发现，然后通过简单的 TCP 连接以长度前缀的格式流式传输 PCM 音频。音频为 48kHz 单声道 Float32。没有服务器，没有互联网，所有数据都保留在本地网络中。应用中有一个语音抑制功能，利用苹果的 SoundAnalysis 框架在设备上检测人声并将其屏蔽。它使用一个滞后门控，关闭时的置信度阈值约为 55%，重新开启时约为 30%，并设有 3 秒的保持时间，以避免声音的抖动。增益的提升是按缓冲区呈指数级的，以避免点击声。效果出乎意料地好。人行道上的对话会被抑制，但你仍然能听到蟋蟀的声音。室内手机使用加速度计检测其是否面朝下且静止（重力.z > 0.85 + 1.75 秒静止缓冲），然后逐渐增强音频。当你拿起手机时，音频会逐渐减弱。整个交互模型基本上是“放下它，忘记它”。没有账户、没有云服务、没有分析、没有录音。零外部依赖。全部使用苹果的框架。免费，无广告，无内购等。我是为自己开发的，觉得其他人也可能会需要这个应用。欢迎提问（不可避免会有人问“我为什么要在 X 城市听外面的声音？” :)）

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Hey HN. I built a small iOS app called Outside In (<a href="https://apps.apple.com/us/app/outside-in/id6759529344">https://apps.apple.com/us/app/outside-in/id6759529344</a>).The idea is simple: you put a spare/old iPhone outside (porch, windowsill, backyard) and keep the other one by your bed. The outside phone captures whatever's happening out there — crickets, rain, wind, the occasional owl — and streams it to the inside phone over your local Wi-Fi. You flip the inside phone face-down and fall asleep to it.I built this because my partner and I used to leave a window cracked at night to hear the outside, but the outside temperature isn't always compatible with that. I wanted the sounds sleeping with the window open without the weather.Some technical details:The phones find each other via Bonjour (NWListener/NWBrowser), then stream PCM audio over a plain TCP connection with length-prefixed framing. 48kHz mono Float32. No server, no internet. Everything stays on the local network.There's a speech suppression feature that uses Apple's SoundAnalysis framework to detect human voices on-device and gate them out. It runs a hysteresis gate with ~55% confidence threshold to close and ~30% to reopen, with a 3-second hold time so it doesn't flutter. The gain ramping is exponential per-buffer to avoid clicks. It works surprisingly well. Conversations on the sidewalk get suppressed but you still hear the crickets behind them.The inside phone uses the accelerometer to detect when it's face-down and still (gravity.z > 0.85 + a 1.75s stillness buffer), then fades audio in. Pick it up and it fades out. The whole interaction model is basically "put it down and forget about it."No accounts, no cloud, no analytics, no recording. Zero external dependencies. All Apple frameworks. Free, no ads, no IAP etc. I built it for myself and figured others might want it too.Happy to answer questions (inevitably some folks who would say "why would I want to listen to outside in X city?" :)

展示HN：Outside In – 将外面的夜间声音实时传输到床边。iOS/免费