From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Lassoff Subject: Re: Soundmodem Not Decoding Real Packets Date: Sat, 2 Jul 2005 04:58:15 +0000 (UTC) Message-ID: References: <20050702040932.4754.qmail@radagast.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-hams-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-hams@vger.kernel.org Dave Platt radagast.org> writes: > Hmmm. > > Which audio drivers are you using - OSS, or ALSA? I've tried both. I'm using the i810_audio module with the AC97 codec for an on-board sound device on a laptop. > I've seen some rather bizarre things with some combinations of card, > driver, and software setting. In particular, problems can occur if: > > [1] The card itself is only capable of supporting a small selection of > sampling rates (many AC97 codes seem to want to run at 48000 > samples/second), and > > [2] You set up the sound modem to use the "natural" sampling rate for > the modulation in question (e.g. 9600 samples/second for 1200-baud > packet), and I cannot seem to find where this is set. Are the specifications for the config file somewhere? > [3] The soundmodem is configured to use /dev/dsp, and > > [4] You're using an ALSA driver with OSS emulation. > > What seems to happen is that the OSS emulation layer quite politely > lies to the soundmodem, says "Sure, 9600 samples/second is supported", > and then tells the ALSA PCM layer to do sample-rate conversion in > software. The ALSA rate converter has some problems, and it ends up > introducing noise into the received audio signal occasionally (usually > on internal buffer boundaries, I believe). The noise is sufficient to > mess up the audio reception. > > The solution to this involves disabling the sample rate conversion > process. I _think_ (but am not sure) that the best way to do this is > to tell the soundmodem to use the ALSA API directly, rather than using > the OSS emulation via /dev/dsp - recent versions of the soundmodem can > do this, and are smart enough to use a sampling rate that the audio > chip supports directly with no conversion being required. Well, from some of the things you have pointed out, I might suspect an audio driver issue, but I'm not sure if the ALSA driver is using OSS emulation with the older i810_audio driver.