diff --git a/src/lib/components/PortTooltip.svelte b/src/lib/components/PortTooltip.svelte
index 565ea230f..4fdfa80b0 100644
--- a/src/lib/components/PortTooltip.svelte
+++ b/src/lib/components/PortTooltip.svelte
@@ -6,7 +6,11 @@
 <script lang="ts">
   import type { InterfaceTemplate, InterfaceType } from "$lib/types";
   import { getPortTooltipState } from "$lib/stores/portTooltip.svelte";
-  import { inferDirection } from "$lib/utils/port-utils";
+  import {
+    inferDirection,
+    inferSignalType,
+    getSignalLabel,
+  } from "$lib/utils/port-utils";
 
   // Get reactive tooltip state from store
   const tooltipState = $derived(getPortTooltipState());
@@ -68,6 +72,15 @@
     return direction ? DIRECTION_LABELS[direction] : null;
   }
 
+  // Signal label: explicit signal_type wins; otherwise inferred from the
+  // connector type plus the (explicit or inferred) direction. Null hides the row.
+  function getSignalTypeLabel(port: InterfaceTemplate): string | null {
+    const direction =
+      port.direction ?? inferDirection(port.type, port.mgmt_only);
+    const signal = port.signal_type ?? inferSignalType(port.type, direction);
+    return signal ? getSignalLabel(signal) : null;
+  }
+
   // Get PoE label
   function getPoELabel(
     poeMode?: "pd" | "pse",
@@ -94,6 +107,9 @@
     {#if getDirectionLabel(port)}
       <div class="port-tooltip-direction">{getDirectionLabel(port)}</div>
     {/if}
+    {#if getSignalTypeLabel(port)}
+      <div class="port-tooltip-signal">{getSignalTypeLabel(port)}</div>
+    {/if}
     {#if port.mgmt_only}
       <div class="port-tooltip-badge mgmt">Management Only</div>
     {/if}
@@ -149,7 +165,8 @@
     font-size: var(--font-size-xs);
   }
 
-  .port-tooltip-direction {
+  .port-tooltip-direction,
+  .port-tooltip-signal {
     color: var(--colour-text-muted-inverse, rgba(255, 255, 255, 0.7));
     font-size: var(--font-size-xs);
   }
diff --git a/src/lib/schemas/index.ts b/src/lib/schemas/index.ts
index 8963f77d1..d0be95985 100644
--- a/src/lib/schemas/index.ts
+++ b/src/lib/schemas/index.ts
@@ -222,6 +222,25 @@ export const InterfacePositionSchema = z.enum(["front", "rear"]);
  */
 export const PortDirectionSchema = z.enum(["input", "output", "bidirectional"]);
 
+/**
+ * Signal type enum - what a port carries, independent of the connector
+ * (spike #1927; #1935). The connector (InterfaceType) describes the plug;
+ * the signal type describes what flows through it (an XLR can carry mic,
+ * line, or AES3). Deliberately starts small; the taxonomy can grow.
+ */
+export const SignalTypeSchema = z.enum([
+  "analog-audio-mic",
+  "analog-audio-line",
+  "analog-audio-speaker",
+  "digital-audio-aes3",
+  "digital-audio-dante",
+  "digital-audio-avb",
+  "digital-video-hdmi",
+  "digital-video-sdi",
+  "clock-word",
+  "control-midi",
+]);
+
 // ============================================================================
 // Container Slot Schemas (v0.6.0)
 // ============================================================================
@@ -302,6 +321,7 @@ export const InterfaceTemplateSchema = z
     poe_mode: PoEModeSchema.optional(),
     poe_type: PoETypeSchema.optional(),
     direction: PortDirectionSchema.optional(),
+    signal_type: SignalTypeSchema.optional(),
   })
   .passthrough();
 
@@ -381,6 +401,7 @@ export const PlacedPortSchema = z
     type: InterfaceTypeSchema,
     label: z.string().max(64).optional(),
     direction: PortDirectionSchema.optional(),
+    signal_type: SignalTypeSchema.optional(),
   })
   .passthrough();
 
@@ -1110,6 +1131,7 @@ export type PoEType = z.infer<typeof PoETypeSchema>;
 export type PoEMode = z.infer<typeof PoEModeSchema>;
 export type InterfacePosition = z.infer<typeof InterfacePositionSchema>;
 export type PortDirection = z.infer<typeof PortDirectionSchema>;
+export type SignalType = z.infer<typeof SignalTypeSchema>;
 export type InterfaceTemplate = z.infer<typeof InterfaceTemplateSchema>;
 export type PowerPort = z.infer<typeof PowerPortSchema>;
 export type PowerOutlet = z.infer<typeof PowerOutletSchema>;
diff --git a/src/lib/types/index.ts b/src/lib/types/index.ts
index f9b5e938c..ced42fe77 100755
--- a/src/lib/types/index.ts
+++ b/src/lib/types/index.ts
@@ -214,6 +214,23 @@ export type InterfacePosition = "front" | "rear";
  */
 export type PortDirection = "input" | "output" | "bidirectional";
 
+/**
+ * Signal type carried by a port, independent of the physical connector.
+ * The connector (InterfaceType) describes the plug; the signal type describes
+ * what flows through it (e.g. an XLR can carry mic, line, or AES3).
+ */
+export type SignalType =
+  | "analog-audio-mic"
+  | "analog-audio-line"
+  | "analog-audio-speaker"
+  | "digital-audio-aes3"
+  | "digital-audio-dante"
+  | "digital-audio-avb"
+  | "digital-video-hdmi"
+  | "digital-video-sdi"
+  | "clock-word"
+  | "control-midi";
+
 // =============================================================================
 // Component Types (NetBox-compatible, schema-only)
 // =============================================================================
@@ -243,6 +260,8 @@ export interface InterfaceTemplate {
   poe_type?: PoEType;
   /** Signal direction. Provides the default used when the placed port omits its own. */
   direction?: PortDirection;
+  /** Signal carried by this port (explicit; inferred from type and direction when unset) */
+  signal_type?: SignalType;
 }
 
 /**
@@ -364,6 +383,8 @@ export interface PlacedPort {
   label?: string;
   /** Signal direction override; falls back to the InterfaceTemplate default when unset */
   direction?: PortDirection;
+  /** Signal override; falls back to the template value, then inference, when unset */
+  signal_type?: SignalType;
 }
 
 /**
diff --git a/src/lib/utils/port-utils.ts b/src/lib/utils/port-utils.ts
index ee9cb6ca5..dd6117ee0 100644
--- a/src/lib/utils/port-utils.ts
+++ b/src/lib/utils/port-utils.ts
@@ -3,7 +3,13 @@
  * Functions for port instantiation when devices are placed
  */
 
-import type { DeviceType, PlacedPort, PortDirection } from "$lib/types";
+import type {
+  DeviceType,
+  InterfaceType,
+  PlacedPort,
+  PortDirection,
+  SignalType,
+} from "$lib/types";
 import { generateId } from "$lib/utils/device";
 
 export type PortCategory = "network" | "power" | "console" | "av";
@@ -106,6 +112,73 @@ export function inferDirection(
   return "bidirectional";
 }
 
+/**
+ * Human-readable signal names, one per SignalType value. Shared source for
+ * every surface that labels signals, so a label change lands everywhere.
+ */
+export const SIGNAL_LABELS: Record<SignalType, string> = {
+  "analog-audio-mic": "Mic level",
+  "analog-audio-line": "Line level",
+  "analog-audio-speaker": "Speaker level",
+  "digital-audio-aes3": "AES3",
+  "digital-audio-dante": "Dante",
+  "digital-audio-avb": "AVB",
+  "digital-video-hdmi": "HDMI",
+  "digital-video-sdi": "SDI",
+  "clock-word": "Word clock",
+  "control-midi": "MIDI",
+};
+
+/**
+ * Label for a signal type, falling back to the raw slug for forward
+ * compatibility if a new value is not yet in SIGNAL_LABELS.
+ */
+export function getSignalLabel(signal: SignalType): string {
+  return SIGNAL_LABELS[signal] ?? signal;
+}
+
+/**
+ * Infer the signal a connector carries from its type (and, for XLR, its
+ * direction: mic level into an input, line level out of anything else).
+ * Returns undefined when the connector implies no distinct signal to label:
+ * network types (ethernet is the connector, not a separate signal), connectors
+ * whose signal has no SignalTypeSchema value yet (DMX, ADAT), and genuinely
+ * ambiguous ones. Device authors set signal_type explicitly for those.
+ */
+export function inferSignalType(
+  type: InterfaceType,
+  direction?: PortDirection,
+): SignalType | undefined {
+  switch (type) {
+    case "xlr-3":
+      return direction === "input" ? "analog-audio-mic" : "analog-audio-line";
+    case "trs-1-4":
+    case "ts-1-4":
+    case "rca":
+    case "db25-audio":
+    case "phoenix":
+      return "analog-audio-line";
+    case "speakon":
+      return "analog-audio-speaker";
+    case "aes3":
+      return "digital-audio-aes3";
+    case "dante":
+      return "digital-audio-dante";
+    case "avb":
+      return "digital-audio-avb";
+    case "hdmi":
+      return "digital-video-hdmi";
+    case "sdi-bnc":
+      return "digital-video-sdi";
+    case "bnc":
+      return "clock-word";
+    case "midi-din":
+      return "control-midi";
+    default:
+      return undefined;
+  }
+}
+
 /**
  * Instantiate ports from a DeviceType's interface templates
  * Creates PlacedPort instances with stable UUIDs for each interface
diff --git a/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.expected.json b/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.expected.json
new file mode 100644
index 000000000..cddb91065
--- /dev/null
+++ b/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.expected.json
@@ -0,0 +1,8 @@
+{
+  "allowList": [
+    {
+      "pathPattern": "\\.position$",
+      "reason": "rail position 3 is converted to internal 1/6U units on load; no coincidental duplicate elsewhere in this fixture unlike the sibling AV fixtures"
+    }
+  ]
+}
diff --git a/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.rackula.yaml b/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.rackula.yaml
new file mode 100644
index 000000000..a3a632ba7
--- /dev/null
+++ b/src/tests/fixtures/upgrade-corpus/v26.7.0-signal-type.rackula.yaml
@@ -0,0 +1,53 @@
+# yaml-language-server: $schema=https://count.racku.la/schemas/rackula-layout.schema.json
+metadata:
+  id: 3f8a1c2d-9e4b-4c7a-8d1f-6b2e9a5c3d71
+  name: Signal Type Demo Rack
+  schema_version: "1.1"
+version: "26.7.0"
+name: Signal Type Demo Rack
+racks:
+  - id: rack-signal
+    name: Signal Demo Rack
+    height: 8
+    width: 19
+    desc_units: false
+    show_rear: true
+    form_factor: 4-post-cabinet
+    starting_unit: 1
+    position: 0
+    devices:
+      - id: dev-signal-demo
+        device_type: signal-demo-device
+        position: 3
+        face: front
+        ports:
+          - id: port-mic-in
+            template_name: Mic In
+            template_index: 0
+            type: xlr-3
+            direction: input
+          - id: port-aes-out
+            template_name: AES Out
+            template_index: 1
+            type: xlr-3
+            direction: output
+            signal_type: digital-audio-aes3
+device_types:
+  - slug: signal-demo-device
+    manufacturer: Acme Audio
+    model: Signal Demo 1U
+    u_height: 1
+    colour: "#8BE9FD"
+    category: av-media
+    interfaces:
+      - name: Mic In
+        type: xlr-3
+        direction: input
+        signal_type: analog-audio-mic
+      - name: AES Out
+        type: xlr-3
+        direction: output
+        signal_type: digital-audio-aes3
+settings:
+  display_mode: label
+  show_labels_on_images: false
diff --git a/src/tests/signal-type.test.ts b/src/tests/signal-type.test.ts
new file mode 100644
index 000000000..92e5d3992
--- /dev/null
+++ b/src/tests/signal-type.test.ts
@@ -0,0 +1,79 @@
+import { describe, expect, it } from "vitest";
+import {
+  InterfaceTemplateSchema,
+  PlacedPortSchema,
+  SignalTypeSchema,
+} from "$lib/schemas";
+import { getSignalLabel, inferSignalType } from "$lib/utils/port-utils";
+import { createTestInterfaceTemplate, createTestPlacedPort } from "./factories";
+import type { SignalType } from "$lib/types";
+
+describe("inferSignalType", () => {
+  it("infers mic level for XLR inputs and line level otherwise", () => {
+    expect(inferSignalType("xlr-3", "input")).toBe("analog-audio-mic");
+    expect(inferSignalType("xlr-3", "output")).toBe("analog-audio-line");
+    expect(inferSignalType("xlr-3")).toBe("analog-audio-line");
+  });
+
+  it("maps analog connectors to line level and speakon to speaker level", () => {
+    expect(inferSignalType("trs-1-4")).toBe("analog-audio-line");
+    expect(inferSignalType("ts-1-4")).toBe("analog-audio-line");
+    expect(inferSignalType("rca")).toBe("analog-audio-line");
+    expect(inferSignalType("db25-audio")).toBe("analog-audio-line");
+    expect(inferSignalType("phoenix")).toBe("analog-audio-line");
+    expect(inferSignalType("speakon")).toBe("analog-audio-speaker");
+  });
+
+  it("maps digital audio, video, clock, and control connectors", () => {
+    expect(inferSignalType("aes3")).toBe("digital-audio-aes3");
+    expect(inferSignalType("dante")).toBe("digital-audio-dante");
+    expect(inferSignalType("avb")).toBe("digital-audio-avb");
+    expect(inferSignalType("hdmi")).toBe("digital-video-hdmi");
+    expect(inferSignalType("sdi-bnc")).toBe("digital-video-sdi");
+    expect(inferSignalType("bnc")).toBe("clock-word");
+    expect(inferSignalType("midi-din")).toBe("control-midi");
+  });
+
+  it("returns undefined when the connector implies no distinct signal", () => {
+    expect(inferSignalType("1000base-t")).toBeUndefined();
+    expect(inferSignalType("console")).toBeUndefined();
+    expect(inferSignalType("dmx-xlr")).toBeUndefined();
+    expect(inferSignalType("adat-optical")).toBeUndefined();
+    expect(inferSignalType("usb-c")).toBeUndefined();
+  });
+});
+
+describe("getSignalLabel", () => {
+  it("labels known signals and falls back to the raw slug", () => {
+    expect(getSignalLabel("analog-audio-mic")).toBe("Mic level");
+    expect(getSignalLabel("clock-word")).toBe("Word clock");
+    expect(getSignalLabel("future-signal" as SignalType)).toBe("future-signal");
+  });
+});
+
+describe("signal_type schema fields", () => {
+  it("accepts signal_type on interface templates and placed ports", () => {
+    const template = InterfaceTemplateSchema.parse(
+      createTestInterfaceTemplate({
+        type: "xlr-3",
+        signal_type: "digital-audio-aes3",
+      }),
+    );
+    expect(template.signal_type).toBe("digital-audio-aes3");
+
+    const port = PlacedPortSchema.parse(
+      createTestPlacedPort({ type: "xlr-3", signal_type: "analog-audio-mic" }),
+    );
+    expect(port.signal_type).toBe("analog-audio-mic");
+  });
+
+  it("rejects unknown signal_type values", () => {
+    expect(SignalTypeSchema.safeParse("laser-show").success).toBe(false);
+    expect(
+      InterfaceTemplateSchema.safeParse({
+        ...createTestInterfaceTemplate(),
+        signal_type: "laser-show",
+      }).success,
+    ).toBe(false);
+  });
+});
diff --git a/static/schemas/rackula-layout.schema.json b/static/schemas/rackula-layout.schema.json
index 35855d113..5c509b26b 100644
--- a/static/schemas/rackula-layout.schema.json
+++ b/static/schemas/rackula-layout.schema.json
@@ -161,6 +161,21 @@
                   ],
                   "type": "string"
                 },
+                "signal_type": {
+                  "enum": [
+                    "analog-audio-mic",
+                    "analog-audio-line",
+                    "analog-audio-speaker",
+                    "digital-audio-aes3",
+                    "digital-audio-dante",
+                    "digital-audio-avb",
+                    "digital-video-hdmi",
+                    "digital-video-sdi",
+                    "clock-word",
+                    "control-midi"
+                  ],
+                  "type": "string"
+                },
                 "type": {
                   "enum": [
                     "100base-tx",
@@ -641,6 +656,21 @@
                       "maxLength": 64,
                       "type": "string"
                     },
+                    "signal_type": {
+                      "enum": [
+                        "analog-audio-mic",
+                        "analog-audio-line",
+                        "analog-audio-speaker",
+                        "digital-audio-aes3",
+                        "digital-audio-dante",
+                        "digital-audio-avb",
+                        "digital-video-hdmi",
+                        "digital-video-sdi",
+                        "clock-word",
+                        "control-midi"
+                      ],
+                      "type": "string"
+                    },
                     "template_index": {
                       "maximum": 9007199254740991,
                       "minimum": 0,
@@ -938,6 +968,21 @@
                         "maxLength": 64,
                         "type": "string"
                       },
+                      "signal_type": {
+                        "enum": [
+                          "analog-audio-mic",
+                          "analog-audio-line",
+                          "analog-audio-speaker",
+                          "digital-audio-aes3",
+                          "digital-audio-dante",
+                          "digital-audio-avb",
+                          "digital-video-hdmi",
+                          "digital-video-sdi",
+                          "clock-word",
+                          "control-midi"
+                        ],
+                        "type": "string"
+                      },
                       "template_index": {
                         "maximum": 9007199254740991,
                         "minimum": 0,