1#!/usr/bin/env python3
2#
3# Copyright 2024 Google LLC
4#
5# Licensed under the Apache License, Version 2.0 (the "License");
6# you may not use this file except in compliance with the License.
7# You may obtain a copy of the License at
8#
9#     http://www.apache.org/licenses/LICENSE-2.0
10#
11# Unless required by applicable law or agreed to in writing, software
12# distributed under the License is distributed on an "AS IS" BASIS,
13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14# See the License for the specific language governing permissions and
15# limitations under the License.
16#
17
18import argparse
19import lc3
20import matplotlib
21import matplotlib.pyplot as plt
22import numpy as np
23import scipy.signal as signal
24
25matplotlib.use('QtAgg')
26
27parser = argparse.ArgumentParser(description='LC3 Encoder')
28
29parser.add_argument(
30    '--frame_duration', help='Frame duration (ms)', type=float, default=10)
31
32parser.add_argument(
33    '--sample_rate', help='Sampling frequency (Hz)', type=float, default=48000)
34
35parser.add_argument(
36    '--hrmode', help='Enable high-resolution mode', action='store_true')
37
38parser.add_argument(
39    '--bitrate', help='Bitrate (bps)', type=int, default=96000)
40
41parser.add_argument(
42    '--libpath', help='LC3 Library path')
43
44args = parser.parse_args()
45
46# --- Setup encoder + decoder ---
47
48fs = args.sample_rate
49
50enc = lc3.Encoder(
51    args.frame_duration, fs, hrmode=args.hrmode, libpath=args.libpath)
52dec = lc3.Decoder(
53    args.frame_duration, fs, hrmode=args.hrmode, libpath=args.libpath)
54
55frame_len = enc.get_frame_samples()
56delay_len = enc.get_delay_samples()
57
58# --- Generate 10 seconds chirp ---
59
60n = 10 * int(fs)
61t = np.arange(n - (n % frame_len)) / fs
62s = signal.chirp(t, f0=10, f1=fs/2, t1=t[-1], phi=-90, method='linear')
63
64# --- Encoding / decoding loop ---
65
66frame_size = enc.get_frame_bytes(args.bitrate)
67bitrate = enc.resolve_bitrate(frame_size)
68
69y = np.empty(len(s) + frame_len)
70
71for i in range(0, len(s), frame_len):
72    y[i:i+frame_len] = dec.decode(enc.encode(s[i:i+frame_len], frame_size))
73
74y[len(s):] = dec.decode(enc.encode(np.zeros(frame_len), frame_size))
75y = y[delay_len:len(s)+delay_len]
76
77# --- Plot spectrograms ---
78
79fig, (ax1, ax2) = plt.subplots(nrows=2, sharex=True)
80
81NFFT = 512
82for (ax, s) in [(ax1, s), (ax2, y)]:
83    ax.specgram(s, Fs=fs, NFFT=NFFT, pad_to=4*NFFT, noverlap=NFFT//2,
84                vmin=-160, vmax=0)
85
86ax1.set_title('Input signal')
87ax1.set_ylabel('Frequency (Hz)')
88
89ax2.set_title(('Processed signal (%.1f kbps)' % (bitrate/1000)))
90ax2.set_ylabel('Frequency (Hz)')
91
92plt.show()
93