performance updates

docs/DJ_WORKSTATION.md

@@ -5,7 +5,7 @@ The main window has two tabs: **Karaoke** and **DJ Studio**. Playback, MIDI hand
 ## Using the decks
 
 - Use the DJ browser’s Import Files / Folder button for DJ music. It has its own `DJ/Library.sqlite`, `DJ/Media` and playlists under the app support folder. It starts empty; existing karaoke songs are not migrated. The tested recursive importer is reused with audio-only import, without CDG graphics. MP3, WAV, M4A, MP4/M4V/MOV audio, AIFF/AIF, CAF, FLAC and AAC extensions are accepted; decoding depends on macOS format support. Imports support progress, cancellation and duplicate detection.
-- Select a DJ library row and use Load A/B, use the row’s A/B buttons, or drag a DJ library song onto a deck. Loading is paused, with no brief autoplay. Finder audio files can also be dropped onto either deck’s header, platter area or centre waveform. Back-to-back drops are queued while a copy/import is running; re-dropping existing media still loads the selected deck. Dropping onto a playing deck asks for confirmation before importing or replacing anything; Cancel preserves playback and Replace & Load explicitly overrides protection. Library loads also respect the active-deck protection preference.
+- Select a DJ library row and use Load A/B, use the row’s A/B buttons or right-click Load into Deck A/B, or drag a DJ library song onto a deck. Loading is paused, with no brief autoplay. Finder audio files can also be dropped onto either deck’s header, platter area or centre waveform. Back-to-back drops are queued while a copy/import is running; re-dropping existing media still loads the selected deck. Dropping onto a playing deck asks for confirmation before importing or replacing anything; Cancel preserves playback and Replace & Load explicitly overrides protection. Library loads also respect the active-deck protection preference.
 - Cyan identifies A; amber identifies B. Each platter’s angle follows actual source playback time, including tempo changes, pauses and seeks. Drag around a platter to jog two source seconds per revolution. This is seek-based jogging, not vinyl scratching.
 - Waveforms come from decoded audio and reuse existing waveform caches. Drag outside an active loop to seek. Green IN/OUT grips resize the loop; dragging inside its region moves it without changing its length. Shift-drag creates a loop in either waveform. Native mouse tracking supports scrubbing in the overview and scrolling spectrum while paused or playing. In the large spectrum, hold the left mouse button and drag left to advance or right to rewind, relative to the initial position without a click jump; the waveform follows the hand. The overview remains an absolute position selector. The scrolling viewport freezes during a drag and resumes following playback afterwards. Waveform scrolling, playheads and platter rotation use the audio clock at up to 60 display frames per second, with interpolated waveform amplitudes.
 - High/mid/low EQ and the bipolar filter are beside each platter. Gain and level knobs have been removed from the on-screen decks. Drag a knob vertically; double-click to reset. Knobs expose adjustable accessibility actions and current values. EQ uses the existing three-band filters; filter is low-pass left, bypass centre, high-pass right.
@@ -73,3 +73,5 @@ The full macOS suite covers karaoke, recursive CDG/audio import, independent DJ
 Attached-interface checks verify available output devices and AUHAL stereo channel maps when the hardware is connected; that check skips when the interface is unavailable. Physical button response, visible LEDs and audible socket isolation still require hands-on verification. Builds compile for arm64 and x86_64; tests execute on Apple silicon. Temporary builds, logs, captures and scripts are kept in task directories under `/private/tmp`, including `kjmix-xml-mappings` and `kjmix-loop-edit`.
 
 Latest validation: **147 tests executed, zero failures, one attached-interface check skipped because the user confirmed the Numark was unplugged**. Earlier attached-interface runs verified the four-channel AUHAL maps; native menu selection and live binding changes are also tested independently of hardware.
+
+Spectrum scrolling caches source-aligned image sections and translates them by fractional pixels as playback advances. On macOS 14+ a view display link schedules refreshes with the current display; macOS 13 uses a timer. Beat and loop markers stay aligned to the same audio-clock position. Cached images are rebuilt after waveform analysis, resize, zoom or colour changes.