OMAP4460 Blaze tablet 4 mic capture has audio capture losses.

Hello Sreenivasa,

1) What is the reason for the audio losses.
3} how can i stop the Audio loss
- I assume that the audio loss is caused by your TinyAlsa configurations. Please provide more information about your use case.

2) What si the maximum data size that can be allocated to store the captured data ( i.e. period_size * number_of_buffers * sizeof( WORD32) ).
- config.format = PCM_FORMAT_S32_LE; Therefore the maximum data size is 32.

unsigned int capture_sample(FILE *file, unsigned int device,
unsigned int channels, unsigned int rate,
unsigned int bits)
{
struct pcm_config config;
struct pcm *pcm;
char *buffer;
unsigned int size;
unsigned int bytes_read = 0;
config.channels = channels;
config.rate = rate;
config.period_size = 1024;
config.period_count = 4;
if (bits == 32)
config.format = PCM_FORMAT_S32_LE;
else if (bits == 16)
config.format = PCM_FORMAT_S16_LE;
pcm = pcm_open(0, device, PCM_IN, &config);
if (!pcm || !pcm_is_ready(pcm)) {
fprintf(stderr, "Unable to open PCM device (%s)\n",
pcm_get_error(pcm));
return 0;
}

Best regards,
Yanko

Hi Yanko,

Thanks for the reply.
I am adding details for your query.

I ) I am using OMAP4 blaze tablet with the OS version 4.1.1 android. I want to capture 4 digital mic signals for beam-forming application.
All the microphone signals are expected to be in sync and without any audio-loss or distortion.

While trying to use tinycap to capture 4 mic signals, I do only tinymix settings. The current tinymix settings are as follows:

"
Number of controls: 73
ctl type num name value
0 ENUM 1 DL1 Equalizer Flat response
1 ENUM 1 DL2 Left Equalizer Flat response
2 ENUM 1 DL2 Right Equalizer Flat response
3 ENUM 1 Sidetone Equalizer Flat response
4 ENUM 1 AMIC Equalizer High-pass 0dB
5 ENUM 1 DMIC Equalizer High-pass 0dB
6 INT 1 DL1 Media Playback Volume 118
7 INT 1 DL1 Tones Playback Volume 120
8 INT 1 DL1 Voice Playback Volume 120
9 INT 1 DL1 Capture Playback Volume 0
10 INT 1 VXREC Media Volume 0
11 INT 1 VXREC Tones Volume 0
12 INT 1 VXREC Voice DL Volume 0
13 INT 1 VXREC Voice UL Volume 0
14 INT 1 AUDUL Media Volume 0
15 INT 1 AUDUL Tones Volume 0
16 INT 1 AUDUL Voice UL Volume 120
17 INT 1 AUDUL Voice DL Volume 0
18 INT 1 SDT UL Volume 101
19 INT 1 SDT DL Volume 120
20 INT 2 DMIC1 UL Volume 149 149
21 INT 2 DMIC2 UL Volume 149 149
22 INT 2 DMIC3 UL Volume 149 149
23 INT 2 AMIC UL Volume 120 120
24 INT 2 BT UL Volume 126 126
25 BOOL 1 DL1 Mono Mixer Off
26 BOOL 1 AUDUL Mono Mixer Off
27 BOOL 1 DL1 MM_EXT Switch Off
28 BOOL 1 DL1 BT_VX Switch Off
29 BOOL 1 DL1 PDM_DL2 Switch On
30 BOOL 1 DL1 PDM Switch Off
31 BOOL 1 Sidetone Mixer Capture Off
32 BOOL 1 Sidetone Mixer Playback On
33 BOOL 1 Capture Mixer Tones Off
34 BOOL 1 Capture Mixer Voice Playback Off
35 BOOL 1 Capture Mixer Voice Capture Off
36 BOOL 1 Capture Mixer Media Playback Off
37 BOOL 1 Voice Capture Mixer Tones Playback Off
38 BOOL 1 Voice Capture Mixer Media Playback Off
39 BOOL 1 Voice Capture Mixer Capture Off
40 BOOL 1 DL1 Mixer Tones On
41 BOOL 1 DL1 Mixer Voice Off
42 BOOL 1 DL1 Mixer Capture Off
43 BOOL 1 DL1 Mixer Multimedia On
44 ENUM 1 MUX_VX1 None
45 ENUM 1 MUX_VX0 None
46 ENUM 1 MUX_UL11 None
47 ENUM 1 MUX_UL10 None
48 ENUM 1 MUX_UL07 None
49 ENUM 1 MUX_UL06 None
50 ENUM 1 MUX_UL05 None
51 ENUM 1 MUX_UL04 None
52 ENUM 1 MUX_UL03 DMic1R
53 ENUM 1 MUX_UL02 DMic2R
54 ENUM 1 MUX_UL01 DMic0R
55 ENUM 1 MUX_UL00 DMic0L
56 INT 2 Capture Preamplifier Volume 1 1
57 INT 2 Capture Volume 4 4
58 INT 2 Aux FM Volume 3 3
59 INT 2 Headset Playback Volume 15 15
60 INT 2 Handsfree Playback Volume 26 26
61 INT 1 Earphone Playback Volume 14
62 ENUM 1 Headset Power Mode Low-Power
63 BOOL 1 Earphone Playback Switch Off
64 BOOL 1 Aux Right Playback Switch Off
65 BOOL 1 Aux Left Playback Switch Off
66 ENUM 1 Headset Right Playback Off
67 ENUM 1 Headset Left Playback Off
68 ENUM 1 Handsfree Right Playback Off
69 ENUM 1 Handsfree Left Playback Off
70 ENUM 1 Analog Right Capture Route Headset Mic
71 ENUM 1 Analog Left Capture Route Headset Mic
72 ENUM 1 TWL6040 Power Mode Low-Power

"

2) With regard to maximum data size, i meant the buffer_size for alsa and not the bit resolution format.
My understanding is that with the larger buffersize audio loss problem can be avoided. But it appears that the product of number_of_periods (-p) and period_size (-n) is limited to about 8000. If it could be more or the bit resolution could be reduced or the sampling rate supported could be reduced , the loss issue could be avoided.

Please advice what should do to avoid this audio loss problem.



Regards,
Sreenivasa

Hello Sreenivasa,

Data from digital microphones can be captured in two ways:

- Directly from the OMAP's DMIC peripheral. Data is recorded at the native params (96 or 192kHz, 32-bits, 4-ch)

- Through the ABE's MM_UL. Data is recorded at the ABE frontend's parameters (e.g. 48kHz, 16-bits, 4-ch)

Which ways do you use in your case?

I believe you are using the ABE's MM_UL frontend as per the tinymix settings.

When you say audio loss, do you mean ALSA overruns? The buffer size of 8000 frames is equivalent to 166ms (assuming recording is at 48kHz). That's a large buffer in my opinion, and shouldn't cause ALSA overruns. Take into account that the larger the buffer the more the latency.

What userspace component is reading the dmic data? The AudioHAL? Have you tried recording using tinycap?

ALSA overruns depend a lot on the pace at which the userspace reads the data from the ALSA buffer. You might want to measure the time taken between the end of a pcm_read() and the start of the next.

Best regards,

Yanko

Hi Yanko,

Thanks for the reply.

1) I use ABE`s MM_UL in my case.

As you mentioned - " Through the ABE's MM_UL. Data is recorded at the ABE frontend's parameters (e.g. 48kHz, 16-bits, 4-ch) ",

but I am not able to capture @ 16 bits / sample in this scenario.
I am using tinycap and I have mentioned the exact tinycap command used by me in the first thread post.

2) I have to clarify about my query.

I did not tell that the buffer size is equivalent to 8000 frames!
I am quoting my tinycap command again.
" tinycap /sdcard/test.pcm -D 0 -d 0 -c 4 -r 48000 -b 32 -p 768 -n 10 "

I would like to know
** Is there a limit on the product of -p and -n?
** why -b 16 is not allowed?


Please reply!

Regards,
Sreenivasa

Yanko,

Thanks for the reply.

By auido losses i mean the ALSA overruns.
How can i prevent them using the tinycap application.

1) Is this a known issue?

2 ) Do you have some standard version of tinycap which i can use. if yes please share it.




Regards,
Sreenivasa

Hello Sreenivasa,

The way to discard media storage latency is mounting a ram disk and recording into it:

# mkdir /data/dmic_rec

# mount -f tmpfs -o size=100m tmpfs /data/dmic_rec

# tinycap /data/dmic_rec/rec.wav -D0 -d0 -r48000 -b32 -c4

How are you checking if ALSA overruns are occurring?

You can check this by:
SND_PCM_STATE_XRUN
The PCM device reached overrun (capture) or underrun (playback). You can use the -EPIPE return code from I/O functions (snd_pcm_writei(), snd_pcm_writen(), snd_pcm_readi(), snd_pcm_readn()) to determine this state without checking the actual state via snd_pcm_state() call. It is recommended to use the helper function snd_pcm_recover() to recover from this state, but you can also use snd_pcm_prepare(), snd_pcm_drop() or snd_pcm_drain() calls.

-EPIPE - This error means xrun (underrun for playback or overrun for capture). The underrun can happen when an application does not feed new samples in time to alsa-lib (due CPU usage). The overrun can happen when an application does not take new captured samples in time from alsa-lib.

Best regards,
Yanko

Hello Sreenivasa,

Do you have progress with check of ALSA overruns?

Best regards,
Yanko

Dear Yanko,

Thanks for the active support.

I will get back after i do the necessary testing.

Thanks.
Regards,
Sreenivasa