Review and repair local recordings with complete outputs
Choose explicit pause, channel, spectrum and frequency operations; verify original frame maps, full matrices and quantized WAV outputs.
Choose an independent task
A recording may need shorter pauses, recovery of a useful channel, inspection of the whole spectrum, or a declared filter chain. Select the operation according to the actual defect. Listen to the source first; a low RMS level does not identify speech or certify that audio is disposable.
| Tool | Operation | Download set |
|---|---|---|
| T269 | Shorten qualifying low-level pauses | PCM16 WAV + complete frame-map JSON/CSV |
| T270 | Select/repeat channels or split all channels | Mapped WAV or channel ZIP + mappings/statistics JSON/CSV |
| T271 | Inspect the complete selected channel | Labelled PNG + full float32 matrix + settings/peaks JSON/CSV |
| T272 | Apply explicit highpass/lowpass/notch sections | PCM16 WAV + response SVG + coefficients/poles/response JSON/CSV |
Shorten pauses and recover channels
T269 compares the maximum channel RMS in rounded20ms windows to the selected threshold, inclusively. Defaults are−40dBFS,500ms minimum pause and200ms retained pause. A10s/8kHz checked example contains80,000 frames; one3s qualifying pause removes22,400 frames, leaving57,600. Retained halves surround the removed middle; the map records exact source/output half-open frame ranges. There is no crossfade. A1s fully quiet example retains1,600 edge frames; a quiet run shorter than the minimum remains untouched.
T270 mapping1,1 sends original channel1 to both outputs without averaging or inferred meaning. The checked stereo source has16,000 frames; both output channels equal its first channel byte for byte. Split-all exports one original channel per mono WAV inside a ZIP. RMS, peak, DC offset and source indexes help compare channels; they do not classify voices.
Read the full spectrum
T271 selects one actual source channel, uses FFT256–4096 with hopFFT/4 and periodic Hann, applies no left padding, and right-zero-pads the final window. One-sided linear amplitude divides by the Hann sum and doubles interior bins. The4s/8kHz/FFT2048 checked example yields60 windows ×1,025 bins =61,500 values. The little-endian float32 matrix contains every value. JSON includes centres, peak tie counts and exact PNG window/bin ranges.
PNG covers the full source duration and Nyquist frequency. Pixels max-pool the represented amplitudes, with empty time columns taking the nearest window. Window centres can extend into the padded tail. Peak ties choose the lowest bin and report their count; peak bins do not estimate speech pitch or identify authenticity. Limits reject the whole operation above4,000,000 cells or100,000,000 FFT work units rather than inspecting only a prefix.
Apply a declared frequency chain
T272 accepts up to8 lines of type,frequencyHz,Q, for example notch,60,10. Supported types are highpass, lowpass and notch; frequency is10Hz through0.49×sample rate and Q0.1–30. Each normalized W3C/RBJ section has strictly stable poles and zero initial state; the same float64 chain runs on every channel, with final float32 conversion.
The checked8s/8kHz recording combines60Hz hum and a1kHz tone. The declared notch suppresses the quantized60Hz component by115.12dB while the1kHz change is−0.000185dB. This deterministic sample establishes the operation, not expected performance on arbitrary recordings. High Q can ring or clip. No gain normalization occurs; coefficients,512 response points and clipping counts are exported.
Understand sample and browser boundaries
Supported inputs are the existing decoder’s WAV depths and MP3,1–8 channels at8–192kHz. Input is limited to30MiB, decoded float32 storage80MiB and complete outputs100MiB; filtering also caps160,000,000 sample-section operations. All generated audio uses round(decoded×32768), clamped to[−32768,32767]. PCM16 kept/selected/split frames remain exact. Float,24/32-bit and MP3 inputs are explicitly quantized rather than preserved in their original format.
MP3 frames and times follow actual browser-decoded PCM. The same48kHz fixture yields96,000 frames/2.000s in Chromium and97,920/2.040s in WebKit due to decoder priming/gapless behaviour. Compare outputs using the report’s decoder, rate and frames, not a promise of equal MP3 duration across browsers.
- Listen to each controlled WAV preview; playback is never automatic. Keep the source for comparison.
- Check complete downloaded mappings/settings rather than treating the200-row result preview as the complete report.
- Lower thresholds or shorten the minimum only with a stated reason; quiet useful content can be removed.
- Correct unsupported headers, invalid parameters or exceeded budgets and rerun; rejection does not produce a successful partial analysis.
- Use the complete response and clipping report when filtering. These tools do not perform speech recognition, automated voice recovery or general denoising.
References
- User task: shortening long pauses in class recordings
Question body read; low-level pause removal is distinct from removing continuous background noise.
- User task: assign the useful left channel to both outputs
Question body read; explicit channel choice is supported without guessing which channel contains speech.
- Developer task: full-file spectrogram instead of current playback buffer
Question body read; complete analysis requires a matrix and full timeline, not a moving display.
- User task: frequency-specific processing of a poor voice recording
Question body read; the hum and low-frequency components match explicit filters; clicks and complete denoising are outside this tool.
- W3C Audio EQ Cookbook
Normalized biquad coefficients and response definitions; technical reference, not independent demand evidence.
Tools in this category
Expand a tool to see its steps, options and supported formats, then open its workspace.
Shorten low-level recording pausesShorten long pauses under an all-channel RMS threshold and export complete retained-frame mappings.
Inspect rounded20ms windows of actual PCM, requiring every channel to be under the threshold. Remove the middle of qualifying pauses while retaining both edges. Download an actual PCM16 WAV and complete quiet/deleted intervals and half-open source/output frame mappings. Retained PCM16 frames are byte-exact without crossfade. This is not speech recognition; useful quiet sounds may be removed.
Steps
- Choose local WAV/MP3.
- Set parameters and inspect actual results,statistics or frame mappings.
- Listen/inspect and download complete outputs.
Available options
- RMS threshold (dBFS)
- -40
- Minimum pause (ms)
- 500
- Retained pause (ms)
- 200
Must be≤minimum; split retained frames as floor-left/ceil-right.
Capabilities and limits
- One supported WAV/MP3 up to30 MiB and80 MiB actual decoded PCM;1–8 channels,8–192kHz; combined downloads100 MiB. WAV uses existing PCM8/16/24/32 and float32/64 support; MP3 must actually decode in the browser. No microphone, upload or remote audio fetch.
- MP3 priming/gapless behavior varies by browser: the same checked MP3 produced2.000s in Chrome and2.040s in WebKit. All times/frames follow this browser’s actual decoded PCM; cross-browser sample/duration identity is not guaranteed. PCM16 output rounds decoded*32768 and clamps[-32768,32767] without normalization; float/24/32/MP3 original encoding bytes are not preserved.
- Threshold−80…−10dBFS; minimum pause100…60,000ms; retained pause20ms up to minimum;10,000 pauses. Threshold comparison is inclusive; the final short window uses its actual samples. Long all-quiet input retains selected edges; input shorter than the minimum is not cut. Zero detections still deliver the original frame sequence.
Recover and split recorded channelsExplicitly isolate, repeat or split existing source channels into playable WAV files with full mappings.
Inspect per-channel RMS, peak, DC and over-full-scale samples, then choose1-based source indexes. Mapping1,1 repeats the left channel on both sides without averaging in right-channel noise. Split every source channel into a ZIP with individual playback. PCM16 selected/repeated/split samples are byte-exact. Channel meaning is not guessed and missing independent stereo cannot be recreated.
Steps
- Choose local WAV/MP3.
- Set parameters and inspect actual results,statistics or frame mappings.
- Listen/inspect and download complete outputs.
Available options
- Delivery mode
- Explicit mapping · Split all source channels
- Source channel list (1-based)
- 1,1
1,1 repeats channel1;2,1 swaps stereo;1 isolates channel1. Ignored in split mode.
Capabilities and limits
- One supported WAV/MP3 up to30 MiB and80 MiB actual decoded PCM;1–8 channels,8–192kHz; combined downloads100 MiB. WAV uses existing PCM8/16/24/32 and float32/64 support; MP3 must actually decode in the browser. No microphone, upload or remote audio fetch.
- MP3 priming/gapless behavior varies by browser: the same checked MP3 produced2.000s in Chrome and2.040s in WebKit. All times/frames follow this browser’s actual decoded PCM; cross-browser sample/duration identity is not guaranteed. PCM16 output rounds decoded*32768 and clamps[-32768,32767] without normalization; float/24/32/MP3 original encoding bytes are not preserved.
- Mapping is a comma list of1–8 output channels and every index must exist; split mode ignores the mapping. Output capacity is checked before allocation; channels are never silently dropped.
Full-recording spectrogram and numeric exportAnalyze the complete recording and export a labelled PNG, full STFT amplitude matrix and explicit window/time/frequency settings.
Select an actual source channel and compute the full periodic-Hann STFT. Download PNG with t[s],f[Hz] and dBFS colour scale, every little-endian float32 amplitude bin, actual window-centre times, peaks and settings. Display may max-pool within image budgets while covering every window; complete numeric data remains downloadable. No recording prefix is silently selected.
Steps
- Choose local WAV/MP3.
- Set parameters and inspect actual results,statistics or frame mappings.
- Listen/inspect and download complete outputs.
Available options
- Source channel (1-based)
- 1
- FFT window samples
- 256 · 512 · 1024 · 2048 · 4096
- Display dBFS floor
- -80
Capabilities and limits
- One supported WAV/MP3 up to30 MiB and80 MiB actual decoded PCM;1–8 channels,8–192kHz; combined downloads100 MiB. WAV uses existing PCM8/16/24/32 and float32/64 support; MP3 must actually decode in the browser. No microphone, upload or remote audio fetch.
- MP3 priming/gapless behavior varies by browser: the same checked MP3 produced2.000s in Chrome and2.040s in WebKit. All times/frames follow this browser’s actual decoded PCM; cross-browser sample/duration identity is not guaranteed. PCM16 output rounds decoded*32768 and clamps[-32768,32767] without normalization; float/24/32/MP3 original encoding bytes are not preserved.
- FFT power-of-two256…4096,hop=FFT/4,no left padding and a zero-padded final window. One-sided amplitude=absFFT/HannSum, doubled except DC/Nyquist. Up to4,000,000 cells and100,000,000 FFT work units, checked before computation. PNG spans full input time, assigns columns by window centres with nearest-window fallback for empty columns, and covers0…Nyquist. Peak bins are amplitude maxima; exact ties choose the lowest bin and report count. This is not pitch or source certification.
Apply explicit recording frequency filtersApply explicit high-pass, low-pass or notch chains and export WAV, response and clipping counts.
Enter type,frequencyHz,Q per line, such as notch,60,10. Apply the same explicit chain to all channels with stable W3C/RBJ biquads and zero initial state. Download an actual PCM16 WAV with complete coefficients,poles,response and before/after levels. No normalization or automatic denoise; high Q can ring, remove useful sounds or cause clipping.
Steps
- Choose local WAV/MP3.
- Set parameters and inspect actual results,statistics or frame mappings.
- Listen/inspect and download complete outputs.
Available options
- Filter chain: type,Hz,Q per line
- notch,60,10
Use highpass,lowpass,notch; up to8 lines,frequencies strictly below Nyquist.
Capabilities and limits
- One supported WAV/MP3 up to30 MiB and80 MiB actual decoded PCM;1–8 channels,8–192kHz; combined downloads100 MiB. WAV uses existing PCM8/16/24/32 and float32/64 support; MP3 must actually decode in the browser. No microphone, upload or remote audio fetch.
- MP3 priming/gapless behavior varies by browser: the same checked MP3 produced2.000s in Chrome and2.040s in WebKit. All times/frames follow this browser’s actual decoded PCM; cross-browser sample/duration identity is not guaranteed. PCM16 output rounds decoded*32768 and clamps[-32768,32767] without normalization; float/24/32/MP3 original encoding bytes are not preserved.
- Up to8 sections and160,000,000 sample-section work units; frequency10Hz…0.49sampleRate,Q0.1…30,finite coefficients and strictly stable poles. Float64 samples/state between sections, final float32 PCM then explicit quantization; samples beyond±1 count as clippedSamples and WAV saturates visibly in the report. Response SVG displays−100…20dB with all512 numeric response points. No speech recognition or full noise restoration.