How to Build a Fair A/B Audio Preview for AI Processing

Two audio players do not make a fair before-and-after test. If the second player restarts from zero or takes half a second to load, the user is no longer comparing two versions of the same moment. They are comparing two memories. That is a weak way to evaluate any audio effect. It is especially weak for AI processing. A denoiser can remove a fan while softening consonants. A de-reverb model can reduce the room tail while making the voice sound less natural. The output may be cleaner without being better. The preview therefore has one job: let the listener switch quickly enough to hear both the improvement and the damage. The rule I use is deliberately boring. Both versions should contain the same edit and play from the same position. Switching should not restart playback or create a pause. The interface should not hint that one version is supposed to win. Two independent <audio> elements fail surprisingly quickly. Each owns its playback state, buffering behavior, clock, and seek operation. The user ends up finding the same position twice and comparing one sound with a memory of another. A better interface has one transport and one version control: [ Play ] [ Original | Processed ] 00:18 ━━━━━━━ 00:42 The transport decides where playback happens. The segmented control decides which signal is audible. One transport, two signals For a short preview, I decode both files into AudioBuffer s, start them at the same AudioContext time and offset, and route each through its own GainNode . Both sources run; only one gain is open. decodeAudioData() decodes complete file data and resamples it to the context's sample rate. The decoded buffers can then share the same audio clock. See the MDN documentation for format and loading details. The core is small: const context = new AudioContext (); const originalGain = context . createGain (); const processedGain = context . createGain (); originalGain . connect ( context . destination ); processedGain . connect ( context . destination )