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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Audio Source configuration |
Date: | Tue, 17 Mar 2015 16:14:51 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 |
Hi Larry, if I understand correctly, then you're using the audio source as "input" to your usrp_sink-terminated flow graph. In that case, the "U"nderruns come from UHD, not the audio source; the flow graph is not supplying samples fast enough. The problem might be systematic, for example if the rate change in your flow graph does not reflect the actual rate ratio between your audio device and the USRP -- e.g. the your audio device generates samples at 48kS/s, and your USRP consumes them with 5MS/s, but you have an interpolation rate of 100 (leading to a rate at which samples arrive at the USRP sink of 4.8MS/s; these are all just exemplary numbers). Also possible, though, is that this is simply an extreme case of clock mismatch: For example, assume the reference clock in your USRP is of by 2ppm, making the "sample consume rate" (1+2e-6) times higher than it should be, according to an imaginary "exact" clock. Now, assume your sound card is a bit "slower" than it should be, so let these should-be 48kS/s be (1-500e-6) times that what it should be. That means that for every a USRP sampling rate of let's say 5MS/s, you'd have around 2500 samples too little per second, which (there's around 250 samples transportable per USB packet) is around 10 sample packets less than the USRP consumes. Greetings, Marcus [1] I pulled up the first sound chip datasheet I could find (TI PCM2903), and it demanded +-500 ppm. On 03/17/2015 03:30 PM, Larry Van Der
Jagt wrote:
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