`nx_rec_grade.nx` source

1// nx_rec_grade.nx -- AUDIO arc, voice-recording thread: grade a recording's
2// technical quality so a bad capture is caught BEFORE it pollutes a voicebank /
3// clone.  Clipping wrecks the LPC spectral envelope; too-quiet kills SNR; a DC
4// offset biases autocorrelation -- all three corrupt every downstream rung, so
5// the recorder gates its own input.
6//
7// Pure integer, NO floats, NO syscalls, NO imports (operates on a caller buffer).
8//
9// Metrics over i16-LE mono PCM s[0..n):
10//   peak     = max |s|
11//   dc       = mean(s)                         (offset)
12//   rms_ac   = sqrt( mean(s^2) - dc^2 )        (AC level, offset removed)
13//   clip_cnt = #{ |s| >= REC_CLIP }            (samples pinned near full-scale)
14//
15// nx_rec_grade(pcm, n, out) -> verdict
16//   out[0]=peak  out[1]=rms_ac  out[2]=dc  out[3]=clip_cnt
17// Verdict priority: CLIPPED > DC_BIAS > TOO_QUIET > TOO_LOUD > GOOD.
18//
19// license_tier: ORIGINAL
20// module: nishi-core.audio.rec_grade
21// capability: AUDIO_RECORDING_QUALITY
22
23import "nx_vecmath.nx"
24const REC_GOOD:       i64 = 0
25const REC_CLIPPED:    i64 = 1
26const REC_DC_BIAS:    i64 = 2
27const REC_TOO_QUIET:  i64 = 3
28const REC_TOO_LOUD:   i64 = 4
29
30const REC_CLIP:       i64 = 32000    // |s| at/above this is clipping
31const REC_CLIP_FRAC:  i64 = 200      // CLIPPED if clip_cnt > n/200 (0.5%)
32const REC_QUIET_RMS:  i64 = 800      // below this AC level = too quiet
33const REC_LOUD_RMS:   i64 = 26000    // above this AC level = clip risk
34
35// integer sqrt (Newton, truncated)
36func _rec_isqrt(x: i64) -> i64 { return vm_isqrt(x) }
37
38func _rec_i16(pcm: *u8, i: i64) -> i64 {
39    let lo: i64 = pcm[i * 2]
40    let hi: i64 = pcm[i * 2 + 1]
41    var v: i64 = lo | (hi << 8)
42    if v >= 0x8000 { v = v - 0x10000 }
43    return v
44}
45
46func nx_rec_grade(pcm: *u8, n: i64, out: *i64) -> i64 {
47    if n < 1 { out[0] = 0; out[1] = 0; out[2] = 0; out[3] = 0; return REC_TOO_QUIET }
48    var sum: i64 = 0
49    var sumsq: i64 = 0
50    var peak: i64 = 0
51    var clip: i64 = 0
52    var i: i64 = 0
53    while i < n {
54        let s: i64 = _rec_i16(pcm, i)
55        sum = sum + s
56        sumsq = sumsq + s * s
57        var a: i64 = s
58        if a < 0 { a = 0 - a }
59        if a > peak { peak = a }
60        if a >= REC_CLIP { clip = clip + 1 }
61        i = i + 1
62    }
63    let dc: i64 = sum / n
64    let meansq: i64 = sumsq / n
65    var var_ac: i64 = meansq - dc * dc
66    if var_ac < 0 { var_ac = 0 }
67    let rms_ac: i64 = _rec_isqrt(var_ac)
68
69    out[0] = peak
70    out[1] = rms_ac
71    out[2] = dc
72    out[3] = clip
73
74    var adc: i64 = dc
75    if adc < 0 { adc = 0 - adc }
76
77    // priority order
78    if clip * REC_CLIP_FRAC > n { return REC_CLIPPED }
79    if adc * 2 > rms_ac { return REC_DC_BIAS }       // offset comparable to signal swing
80    if rms_ac < REC_QUIET_RMS { return REC_TOO_QUIET }
81    if rms_ac > REC_LOUD_RMS { return REC_TOO_LOUD }
82    return REC_GOOD
83}
nx_rec_grade.nx source

`nx_rec_grade.nx` source
