From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clemens Ladisch Subject: Re: IEC switch issues Date: Wed, 23 Jun 2010 17:10:01 +0200 Message-ID: <4C2223C9.2080602@ladisch.de> References: <4C21F88C.6000200@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from out2.smtp.messagingengine.com (out2.smtp.messagingengine.com [66.111.4.26]) by alsa0.perex.cz (Postfix) with ESMTP id 75B7F244A4 for ; Wed, 23 Jun 2010 17:10:05 +0200 (CEST) In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: pl bossart Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org pl bossart wrote: >>> If I play my AC3 data on my HDAudio/SPDIF output using the hw:0,1 >>> device, I can use alsamixer/amixer to mute/unmute. >>> >>> Now if I use the iec958: plugin, I can't control the mute switch any longer: >> >> Muting an AC-3 stream would require encoding a stream of silent PCM >> samples (no data is not the same as silence); therefore, the iec958 >> plugin disallows muting. > > Actually the problem happens also with plain PCM rendered on the > iec958 device.There's no way to use the IEC switch. > So why do we have an S/PDIF switch in the first place? Because the hardware has this switch; the driver just exposes all hardware features. > If it cannot be used when you sent IEC-formatted data (be that PCM > or AC3-formatted data), then why bother? Some codecs allow looping back the ADC output to the SPDIF transmitter. In these cases, disabling the SPDIF transmitter might be useful. Regards, Clemens