# Codec Artifact Detector Compare an original master with its lossy encode and flag pre-echo, transient smearing, bandwidth loss and stereo damage, with per-event timestamps. > Canonical page: https://elysiatools.com/en/tools/audio-codec-artifact-detector - **Category:** Media - **Keywords:** codec artifact, pre-echo, smearing, bandwidth loss, lowpass, joint stereo, mp3 quality, aac quality, opus, residual analysis, full reference, encode check, transient blur, side channel, lossy codec ## Overview A full-reference check of what a lossy codec did to your audio: upload the original master and the encoded file you want to inspect (an MP3, AAC or Opus download, or your own encode), and the detector aligns the two in time and level, then reads the residual (original minus decoded encode) the way codec engineers audition it. Four artifact families are measured with the mechanisms described in the AES perceptual-audio-coding literature: PRE-ECHO — block-based coders quantize a whole analysis block, so the quantization noise of a transient spreads backwards and “announces” the attack; the tool finds sharp attacks that rise out of a quiet lead-in and reports how much noise the encode added in the 30 ms before each onset. TRANSIENT SMEARING — the attack sharpness of each transient is compared between original and encode, so a slowed, rounded attack shows up as attack loss in dB. BANDWIDTH LOSS — long-term average spectra of both sides give each an effective bandwidth (50 dB down from spectral peak); lossy encoders low-pass their input, and the loss in Hz plus the third-octave band deltas show where the top end went. STEREO DAMAGE — side-channel (L minus R) energy and the inter-channel correlation are compared, exposing joint-stereo collapse. The report grades every family (none / minor / notable / severe) and lists the worst events with timestamps so you can jump straight to the damaged spots in your DAW. These are energy-based indicators on the decoded signal, not a PEAQ/ODG perceptual score: they tell you where to listen, and encoders differ, so verify by ear before rejecting a delivery. ## Inputs - **Original audio (reference)** (file) - **Encoded audio to inspect** (file) - **Sensitivity** (select) - **Analysis window (seconds)** (number): e.g. 240 ## When to use - Auditioning deliverables from streaming platforms, podcast hosts, or distributors to verify encode transparency against your master. - Tuning encoder presets, bitrates, or formats (MP3 vs. AAC vs. Opus) during post-production to identify aggressive transient smearing or bandwidth roll-off. - Troubleshooting joint-stereo image collapse or phase cancelation issues introduced during lossy audio compression. ## How it works - The tool accepts an uncompressed reference file and an encoded audio file, automatically matching their playback alignment and leveling. - It computes the residual signal by subtracting the decoded stream from the reference audio to expose quantization noise and discarded spectral data. - Perceptual mechanisms evaluate pre-onset noise in a 30 ms window before sharp attacks, transient sharpness deltas, high-end spectral bandwidth cutoffs, and side-channel correlation. - An HTML diagnostic report is produced, scoring each artifact category from 'none' to 'severe' with exact timestamps for each flagged defect. ## Use cases - Mastering quality control: checking whether aggressive limiting combined with AAC/MP3 encoding creates audible transient pre-echo on drum tracks. - Codec benchmarking: comparing AAC, Opus, and MP3 outputs at 96 kbps, 128 kbps, and 192 kbps to find the minimum transparent bitrate for voice and acoustic instruments. - Archive validation: inspecting re-encoded delivery files against source PCM assets to document high-frequency bandwidth truncation. ## Frequently asked questions ### What audio file types are supported? You can upload any standard audio file supported by your browser, including uncompressed WAV or AIFF files and lossy formats like MP3, AAC, or Opus up to 100 MB. ### Does this tool provide a PEAQ or ODG score? No. It calculates physical energy-based indicators across four specific artifact families rather than an estimated PEAQ or ODG perceptual score. ### How does the detector measure pre-echo? It locates sharp transients preceded by quiet segments and measures how much backward-spread quantization noise was introduced into the 30 milliseconds before the transient onset. ### What does stereo damage indicate in the report? Stereo damage flags differences in side-channel (L minus R) energy and inter-channel correlation, pinpointing stereo image narrowing or joint-stereo collapse. ### How does the sensitivity setting change results? Sensitivity adjusts the threshold for flagging events: 'strict' reports subtle variations, 'standard' catches clear audibility issues, and 'lenient' filters out all but significant degradation. ## Related tools - [Lossy Codec Preview Compare](https://elysiatools.com/en/tools/audio-lossy-preview-compare): Hear and measure what streaming does to your master: encode to MP3, AAC or Opus at real streaming bitrates, decode back, and compare loudness shift, true-peak overshoot and headroom against the original — the Apple Digital Masters round-trip audition as a report plus downloadable preview files. - [Podcast Chapter Marker Builder](https://elysiatools.com/en/tools/podcast-chapter-marker-builder): Build every podcast chapter format from one timecoded list: Podcasting 2.0 JSON + RSS tag, ID3v2.4 CHAP+CTOC burned into an MP3, Vorbis comments, mp4chaps, YouTube timestamps and SRT, with a per-player support matrix. - [Audio Chord Progression Detector](https://elysiatools.com/en/tools/audio-chord-progression-detector): Estimate an audio file's chord sequence locally and download CSV, JSON, SVG, and method notes in one ZIP. - [Audio Set CBR](https://elysiatools.com/en/tools/audio-set-cbr): Re-encode audio using Constant Bitrate (CBR) - [Batch Audio Converter](https://elysiatools.com/en/tools/audio-batch-converter): Convert multiple audio files between different formats like MP3, WAV, FLAC, AAC, OGG, Opus with quality settings and batch processing - [Audio Codec Swap](https://elysiatools.com/en/tools/audio-codec-swap): Change the codec of an audio file within a chosen output format - [Audio Profile Setter](https://elysiatools.com/en/tools/audio-profile-setter): Set a specific encoding profile (e.g., AAC-LC, HE-AAC, Opus voice/audio) - [WAV Compress](https://elysiatools.com/en/tools/wav-compress): Compress a WAV file by converting to MP3, AAC, OGG, or Opus ## Samples - [Copyright-Free FLAC Audio Samples](https://elysiatools.com/en/samples/flac-samples): Lossless FLAC audio samples for testing and development, mirrored from MP3 set with nature sounds and meditation music - [Copyright-Free MP3 Audio Samples](https://elysiatools.com/en/samples/mp3-samples): Collection of royalty-free audio samples for testing and development purposes including nature sounds, meditation music, and ambient audio - [Copyright-Free WAV Audio Samples](https://elysiatools.com/en/samples/wav-samples): Uncompressed PCM WAV audio samples for testing and development, mirrored from MP3 set with nature sounds and meditation music - [Copyright-Free OPUS Audio Samples](https://elysiatools.com/en/samples/opus-samples): Next-generation OPUS audio samples with superior compression and quality, featuring nature sounds and meditation music optimized for modern streaming