[PATCH] cmipci - utilize ADC48K44K bit

From: "Timofei V. Bondarenko" <tim@ipi.ac.ru>
To: alsa-devel@alsa-project.org
Subject: [PATCH] cmipci - utilize ADC48K44K bit
Date: Wed, 07 Nov 2007 15:08:19 +0300	[thread overview]
Message-ID: <4731AAB3.5000209@ipi.ac.ru> (raw)

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Hi.

Setting the ADC48K44K greatly improves capture quality at 48k sampling rate.

With this bit clear ADC does ZOH interpolation of every 22th sample at 48k.

At frequencies higher than 48k there ADC performs a little better with 
ADC48K44K bit set.
At 44.1k ADC performs a little better with this bit clear.
At frequencies below 44.1k there is no difference.


Regards,
	Tim.

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Signed-off-by: Timofei Bondarenko <tim@ipi.ac.ru>

--- alsa-driver-hg20071107/alsa-kernel/pci/cmipci.c	2007-11-01 04:00:07.000000000 +0300
+++ alsa-driver/alsa-kernel/pci/cmipci.c	2007-11-07 14:55:05.000000000 +0300
@@ -869,6 +869,13 @@ static int snd_cmipci_pcm_prepare(struct
 	snd_cmipci_write(cm, CM_REG_CHFORMAT, val);
 	//snd_printd("cmipci: chformat = %08x\n", val);
 
+	if (!rec->is_dac && cm->chip_version) {
+		if (runtime->rate > 44100)
+			snd_cmipci_set_bit(cm, CM_REG_EXT_MISC, CM_ADC48K44K);
+		else
+			snd_cmipci_clear_bit(cm, CM_REG_EXT_MISC, CM_ADC48K44K);
+	}
+
 	rec->running = 0;
 	spin_unlock_irq(&cm->reg_lock);
 


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