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Correct downsampling

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This commit is contained in:
Matt
2025-12-14 09:59:33 +00:00
parent 1c29d37c6f
commit 855d287e1d
1 changed files with 21 additions and 9 deletions
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30
main/index.js
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@@ -19,8 +19,9 @@ let activeConfig = {
let lowRateState = { let lowRateState = {
accMin: 4096, accMin: 4096,
accMax: 0, accMax: 0,
count: 0, accMax: 0,
targetCount: 1 progress: 0.0,
targetCount: 1.0
}; };
// Approximate full-scale voltages for ESP32C6/ESP32 ADC attenuations // Approximate full-scale voltages for ESP32C6/ESP32 ADC attenuations
@@ -74,7 +75,8 @@ function calculateTimeOffset(offsetX, effectiveSampleRate) {
function resetLowRateState() { function resetLowRateState() {
lowRateState.accMin = 4096; lowRateState.accMin = 4096;
lowRateState.accMax = 0; lowRateState.accMax = 0;
lowRateState.count = 0; lowRateState.accMax = 0;
// NOTE: We do NOT reset progress to maintain fractional phase alignment across packets
} }
// Helper function to schedule WebSocket reconnection // Helper function to schedule WebSocket reconnection
@@ -227,21 +229,31 @@ function processData(/** @type Uint16Array */newData) {
// Passthrough mode // Passthrough mode
pushToBuffer(newData); pushToBuffer(newData);
} else { } else {
// Accumulation mode (Peak Detect) // Accumulation mode (Peak Detect) with Fractional Resampling
let pointsToPush = new Uint16Array(newData.length * 2); // Worst case let pointsToPush = new Uint16Array(newData.length * 2); // Worst case
let idx = 0; let idx = 0;
// We add 1.0 "samples worth" of progress for each input sample.
// When progress >= targetCount, we have enough input density to emit an output point.
// We subtract targetCount (rather than reset to 0) to preserve fractional error (dither/phase).
for (const val of newData) { for (const val of newData) {
if (val < lowRateState.accMin) lowRateState.accMin = val; if (val < lowRateState.accMin) lowRateState.accMin = val;
if (val > lowRateState.accMax) lowRateState.accMax = val; if (val > lowRateState.accMax) lowRateState.accMax = val;
lowRateState.count++;
if (lowRateState.count >= lowRateState.targetCount) { lowRateState.progress += 1.0;
if (lowRateState.progress >= lowRateState.targetCount) {
// Push min and max to draw a vertical line // Push min and max to draw a vertical line
pointsToPush[idx++] = lowRateState.accMin; pointsToPush[idx++] = lowRateState.accMin;
pointsToPush[idx++] = lowRateState.accMax; pointsToPush[idx++] = lowRateState.accMax;
// Reset // Reset Min/Max for next window
resetLowRateState(); lowRateState.accMin = 4096;
lowRateState.accMax = 0;
// Subtract one full window's worth of progress
lowRateState.progress -= lowRateState.targetCount;
} }
} }
if (idx > 0) { if (idx > 0) {
@@ -361,7 +373,6 @@ function draw() {
ctx.strokeStyle = '#4ade80'; ctx.strokeStyle = '#4ade80';
ctx.lineWidth = 2; ctx.lineWidth = 2;
const step = w / (maxPoints - 1);
const maxAdcVal = 4096; // 12-bit fixed scale const maxAdcVal = 4096; // 12-bit fixed scale
// Trigger values // Trigger values
@@ -374,6 +385,7 @@ function draw() {
} }
} }
let step = w / (maxPoints - 1);
drawData.forEach((val, i) => { drawData.forEach((val, i) => {
const x = i * step; const x = i * step;
const y = h - (val / maxAdcVal * h); const y = h - (val / maxAdcVal * h);