[alsa-devel] [PATCH utils] aplay: fix VU meter for S24_LE etc formats

[Ricard Wanderlof]

When recording or playing back audio in a format where the number of 
significant bits is less than the physical width (e.g. S24_LE), the VU 
meter code needs to consider the number of significant bits in the samples 
rather than the physical sample width (e.g. 24 vs 32 bits). Otherwise the 
resulting VU meter display will be far too low and it will just indicate 
0% all the time.

Tested with a device supporting the S24_LE format.

Signed-off-by: Ricard Wanderlof <ricardw at axis.com>
---
 alsa-utils/aplay/aplay.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/aplay/aplay.c b/aplay/aplay.c
index e58e1bc..19b6a92 100644
--- a/aplay/aplay.c
+++ b/aplay/aplay.c
@@ -124,7 +124,7 @@ static int fatal_errors = 0;
 static int verbose = 0;
 static int vumeter = VUMETER_NONE;
 static int buffer_pos = 0;
-static size_t bits_per_sample, bits_per_frame;
+static size_t significant_bits_per_sample, bits_per_sample, bits_per_frame;
 static size_t chunk_bytes;
 static int test_position = 0;
 static int test_coef = 8;
@@ -1344,6 +1344,7 @@ static void set_params(void)
 		snd_pcm_dump(handle, log);
 
 	bits_per_sample = snd_pcm_format_physical_width(hwparams.format);
+	significant_bits_per_sample = snd_pcm_format_width(hwparams.format);
 	bits_per_frame = bits_per_sample * hwparams.channels;
 	chunk_bytes = chunk_size * bits_per_frame / 8;
 	audiobuf = realloc(audiobuf, chunk_bytes);
@@ -1745,7 +1746,7 @@ static void compute_max_peak(u_char *data, size_t count)
 		}
 		return;
 	}
-	max = 1 << (bits_per_sample-1);
+	max = 1 << (significant_bits_per_sample-1);
 	if (max <= 0)
 		max = 0x7fffffff;
 
-- 
1.7.10.4


-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30