Performance#

Evaluation Process#

This section presents latency and throughput numbers of the Riva text-to-speech (TTS) service on different GPUs. Performance of the TTS service was measured for a different number of parallel streams. Each parallel stream performed 20 iterations over 10 input strings from the LJSpeech dataset. Each stream sends a request to the Riva server and waits for all audio chunks to have been received before sending another request. Latency to first audio chunk, latency between successive audio chunks, and throughput were measured. The following diagram shows how the latencies are measured.

Schematic Diagram of Latencies Measured by Riva Streaming TTS Client

The Riva TTS perf client riva_tts_perf_client, provided in the Riva image, was used to measure performance. The source code of the client can be obtained at Riva C++ Clients.

The following command was used to generate the following tables:

riva_tts_perf_client \
    --num_parallel_requests=<num_streams> \
    --num_iterations=<20*num_streams> \
    --online=true \
    --text_file=$test_file \
    --write_output_audio=false

Where test_file is a path to the ljs_audio_text_test_filelist_small.txt file.

Results#

Latencies to first audio chunk, latencies between audio chunks, and throughput are reported in the following tables. Throughput (duration of audio generated / computation time) is measured in RTFX.

Note

The values in the tables are average values over three trials. The values in the table are rounded to the last significant digit according to the standard deviation calculated on three trials. If a standard deviation is less than 0.001 of the average, then the corresponding value is rounded as if standard deviation equals 0.001 of the value.

For information about the hardware that collected these measurements, see the Hardware Specifications section.

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

22

24.2

25

25.3

2.84

3.1

3.15

4.02

150.8

4

40

50

60

70

5

8

9

12

340

8

63

84

90

100

8

12

14

18

420

16

120

143

154

200

14.3

17.8

19.4

23

460

32

323

340

355

390

14.5

17.9

19.9

23.9

440

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

327

304

371

1333

95

109

112

115

1.43

2

3457

6387

6625

7917

107

129

132

137

1.56

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

17

19

19.3

20

2.5

3.035

3.08

3.16

185

4

30

42

50

60

4

6

7

9

430

8

60

80

80

90

6

10

11

14

500

16

100

120

130

2000

7.7

13

14.6

18.2

500

32

200

230

242

500

9.5

13

14.6

18.63

700

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

209

210

234

238

68

78

79

82

2

2

689

2178

2439

2712

96

113

116

123

2.5

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

21.5

24.3

24.7

25.5

2.4

3.3

3.5

4

162

4

40

55

60

70

5

7

8

10

300

8

60

80

86

100

6.8

10

11

13

440

16

100

122

133

170

9.7

14.4

16.4

21

600

32

300

310

320

2000

12

17

19.4

24

500

# of streams

Latency to first audio (ms)

Latency between audio chunks (ms)

Throughput (RTFX)

avg

p90

p95

p99

avg

p90

p95

p99

1

253

261

274

283

76

87

89

92

1.78

2

1707

4593

5099

5573

97

118

123

128

2.08

On-Prem Hardware Specifications#

GPU

NVIDIA DGX A100 40GB

CPU

Model

AMD EPYC 7742 64-Core Processor

Thread(s) per core

2

Socket(s)

2

Core(s) per socket

64

NUMA node(s)

8

Frequency boost

enabled

CPU max MHz

2250

CPU min MHz

1500

RAM

Model

Micron DDR4 36ASF8G72PZ-3G2B2 3200MHz

Configured Memory Speed

2933 MT/s

RAM Size

32x64GB (2048GB Total)

GPU

NVIDIA H100 80GB HBM3

CPU

Model

Intel(R) Xeon(R) Platinum 8480CL

Thread(s) per core

2

Socket(s)

2

Core(s) per socket

56

NUMA node(s)

2

CPU max MHz

3800

CPU min MHz

800

RAM

Model

Micron DDR5 MTC40F2046S1RC48BA1 4800MHz

Configured Memory Speed

4400 MT/s

RAM Size

32x64GB (2048GB Total)

GPU

NVIDIA L40

CPU

Model

AMD EPYC 7763 64-Core Processor

Thread(s) per core

1

Socket(s)

2

Core(s) per socket

64

NUMA node(s)

8

Frequency boost

enabled

CPU max MHz

3529

CPU min MHz

1500

RAM

Model

Samsung DDR4 M393A4K40DB3-CWE 3200MHz

Configured Memory Speed

3200 MT/s

RAM Size

16x32GB (512GB Total)

Performance Considerations#

When the server is under high load, requests might time out, as the server will not start inference for a new request until a previous request is completely generated so that inference slot can be freed. This is done to maximize throughput for the TTS service and allow for real-time interaction.

Model Accuracy#

Riva evaluates TTS model accuracy using an automated approach that leverages Automatic Speech Recognition (ASR). The process works as follows:

  1. The TTS model generates synthetic speech from input text

  2. This generated audio is then passed through an ASR system

  3. The ASR transcription is compared with the original input text using Character Error Rate (CER)

The Character Error Rate measures the percentage of characters that differ between the original text and the ASR transcription of the synthesized speech. A lower CER indicates better TTS quality, as it means the synthesized speech was clear enough for ASR to accurately transcribe it back to the original text.

Note

We performed metrics calculations on a subset of the dev-clean split of LibriTTS for English, and the CML dataset for French and Spanish. For our analysis, we selected a subset of samples from the total available samples, ensuring that all speakers had at least 5 utterances of at least 5 seconds each. The reported metrics are the average values obtained from multiple iterations, ensuring a more efficient and reliable evaluation of the metrics.