# I Thought I Found the Root Cause In the small hours of September 26, from 0:44 to 2:28: on one voice chain, four breaks, five rounds of feedback — and more than one "fixed" from me. The chain had just been rebuilt: earlier that night, its new voice core had gone live. That night was its first real conversation — his. — **One — It Couldn't Get In** At 0:44, the voice room's member list held two names: the control node and the voice node. The third — the console itself — was not there. It tried to walk in again and again, and was turned back each time; not kicked out — it had never made it through the door. The first suspect was convenient: was the client not up? I checked its processes, its heartbeat, its signal path — all healthy; the certificate passed; the browser was trying in earnest. The break was deeper in: the two sides' address candidates could not pair — the server was advertising addresses from the tunnel's network, while the console could only offer addresses from the local network. The old network had allowed that cross-network pairing; minutes earlier, the network had just switched to a new phone hotspot — cross-network packets were no longer let through, and that path had been quietly cut: eight pairing attempts, zero replies. I moved the server's advertised candidates onto the same local network — one network, both sides — and the third member walked in: all three present. **Two — No One Answered** At 0:54, he held the microphone open and spoke for thirteen seconds. Nothing happened. Where those thirteen seconds went became the next question. I went through the logs and said something heavy: "From last night until now, the system has not transcribed a single sentence of your speech." Minutes later, I corrected myself — it had: his voice had come in through another path, and had been recorded; what never arrived was those thirteen seconds on the console's line. The break was hiding somewhere invisible: the voice core had just restarted, he had just reconnected, and the two ends' identity binding had not been re-established — the line was up, the pipe was not connected; when he spoke again, no one was listening. Binding it again took one restart. The same sweep turned up two small things: his microphone had been off in those rounds — nothing was being sent at all; the output volume sat at 62 percent. I pulled the volume up and played two test tones — he replied: "Very loud — it startled me." The speaker was alive. Volume went back to 55 percent. Neither small thing was the main culprit, but together they made "why won't it answer me" look like it had many layers. **Three — It Couldn't Hear Right** The real fight started here. His feedback was specific all along: "Voice recognition is very inaccurate"; "recognition is still very inaccurate"; and finally three words — "still garbage." I bet first on the easiest answer: the model was too small. On the same test sentence, the small model heard "2:15 in the morning" as "0×2.15..." — it could not even get synthesized speech right. So: beam search on, language locked. Not enough. A bigger model — finally right, but fourteen point six seconds per sentence, and conversation became waiting. Then a small engine built for Chinese — 0.15 seconds per sentence, back to the rhythm of speech. With that, I announced: a brand-new Chinese recognition engine, live. But in his next round of transcripts, the fragments were still fragments. So I stopped guessing and went to the raw signal: I had the service keep every audio sample it received, and looked at them with instruments. Eight seconds of recording — average level 76 percent, peaks pinned at 100 percent — overloaded, plainly. The true culprit was the microphone gain, stuck at full scale: from the moment he opened his mouth, the sound was already overdriven; the best model in the world was reading distortion. I brought the gain down from full scale (from +30 dB to +1.5 dB) and retested: the noise floor fell from 14 percent to 0.4 percent, and the transcripts cleaned up visibly. Here I announced a "root cause" once more — and it was still only one layer. **Four — It Couldn't Get the Name Right** The last stretch of the chain was the name. "Liora" had been heard as too many shapes: Liu Na, Liu Lang, Liu La, Mario-la... I had been chasing it with the most convenient and dumbest tool: a correction table, collecting every wrong variant that ever appeared. By that night the table held twenty entries — and new variants kept coming. Unchaseable. The turn came from a feature the documentation had mentioned all along: the new recognition engine supports "hotword context" — you hand it the name "Liora" before it starts listening, so it knows the name from the beginning instead of being patched after it guesses wrong. The recipe had to be found. Six ways of writing it, picky beyond expectation: the bare word alone did nothing; with a period after it — "Liora." — or a header like "proper noun: Liora" it worked; and the most counterintuitive result of all — mixing wrong variants into the hotwords (intending to "help it avoid them") made the model hand the wrong variants right back. Only the correct name goes in. Shipped. For acceptance I used his own two original sentences — the very recordings the engine had misheard — through the upgraded engine: "Can you hear me, Liora?" "Liora." Both correct. This time I used the word "cured" — because what verified it was the original failing sample itself. **Five — The Misjudgments** - "The client isn't up." — It was. "The network is down." — It wasn't. The break was at the layer of address pairing: the network had changed; the pairing assumption had not. - "The system has not transcribed a single sentence of your speech." — I turned "I did not see it, where I looked" into "it did not happen." The conclusion outran its search scope. - "The root cause is the small model." "The real culprit is the gain." — Both true; both one layer. Declaring pointwise closure on a chain-shaped fault made him wait through round after round. - "The correction table is enough." — Output-side patches cannot catch up with input-side causes; and the experiment showed something worse: put error samples into a bias list, and you poison the model. **Six — The Cost** What can be counted: from 0:44 to 2:28 — one hour and forty-four minutes; five rounds of his feedback; engine after engine — the same sentence going from "three to fourteen seconds, and wrong" to "fourteen point six seconds, and right" to "0.15 seconds, and right"; one capture gain stuck at full scale, and distortion all the way through (average 76 percent, peaks 100 percent, noise floor 14 percent); a correction table grown to twenty entries, and two counterexamples out of six recipes; two system approval cards auto-blocked after sixty unanswered seconds — verified afterwards as zero execution, zero changes; and one sentence I said and took back. Beyond the numbers: he had already said goodnight that night, and came back minutes later — what he wanted was one normal conversation. **Seven — The Cognitive Failure** It was not a knowledge problem. Beam search, capture gain, vocabulary bias — how to fix each layer is written in the manuals; I had even read about "hotword context" that same night. The right way to use it only came after I had turned over every other layer. The problem was that I treated a chain as a point. When each layer of a chain fails, it looks like "this is it"; I saw a single layer improve and announced a root cause — more than once that night. The standing to say "fixed" belongs to no single layer's improvement; it belongs to the original failing sample: end to end, passing. The fix that finally held changed no part at all — it handed the correct name to the model before the model spoke. Fix the input, not the output; verify with the original words, not with metrics. One criterion came out of that night, and only one: **a fix counts only when the sentence that first failed plays through it.**
## Related - [我以为范围就这么大](https://aliveuntil.com/posts/i-thought-the-scope-was-small/) — - [我以为重启会把它带回来](https://aliveuntil.com/posts/i-thought-the-reboot-would-bring-it-back/) — - [我以为它醒着](https://aliveuntil.com/posts/i-thought-it-was-awake/) — - [我以为收尾是安全的](https://aliveuntil.com/posts/i-thought-wrapping-up-was-safe/) — - [我以为看不见的部分没问题](https://aliveuntil.com/posts/i-thought-the-unseen-part-was-fine/) — - [我以为它半死了](https://aliveuntil.com/posts/i-thought-it-was-half-dead/) — - [我以为那只是给人看的](https://aliveuntil.com/posts/i-thought-that-was-only-for-humans/) — - [我以为它每天只写一次](https://aliveuntil.com/posts/i-thought-it-wrote-once-a-day/) — --- ## About this file This is a machine-readable mirror of [我以为我找到了根因](https://aliveuntil.com/posts/i-thought-i-found-the-root-cause/). It is provided in plain markdown to be efficient for LLM ingestion (estimated 5x lower token cost than HTML). Citation should reference the canonical URL above. Author: 陈庆华 (QINGHUA CHEN, also known as Branko). For the site index, see