2010/5/21 James Courtier-Dutton james.dutton@gmail.com
On 20 May 2010 10:41, Sebastian H. vand2@gmx.de wrote:
That's clear. I imagined that maybe the dB scale could be the "real thing" and the
volume
steps would be a convenient but possibly coarse mapping into a denser stepped dB space provided by the hardware/driver. This was unlikely but I wanted to ask anyway ;-).
I believe it could be extended to support a continuous range. For example, some hardware uses a 32bit value to control the gain. The mix operation is simply "the_sample" * "the_control_value". So in this case the hardware has a linear control that can be considered continuous for our purposes. The conversion from the control value to a usable value would have to include a user land log operation. It was never implemented due to lack of demand. For the cards that do have this 32bit linear value, a simple lookup table is used in the kernel code to convert it to 256 step values. If implemented, one could then introduce professional gain controls that do not produce "clicks" in the output when adjusted. gain controls with steps in them produce clicks when the gain control is adjusted.
For example , the 10 band stereo graphic equalizer of au8830 has 32678 steps but the dB range is most likely between -6dB and +6dB
I have not measured the dB values but there is no clipping occur at maximum gain
just compared with the software equalizer alsaequal where you can hear distortion quite easily
snd_vortex_eq_info(struct snd_kcontrol *kcontrol, struct snd_ctl_elem_info *uinfo) { uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER; uinfo->count = 2; uinfo->value.integer.min = 0x0000; uinfo->value.integer.max = 0x7fff; return 0; }
How can I implement a dB scale for those 10 EQ gain/atten controls ?