![]() We're looking at playing back 192Khz sampled HD audio as well as the common 44.1Khz audio. ![]() If Freescale had just added a couple more bits of precision. However, not having accurate audio clocks is a fatal flaw. Six serial controllers (4 of which can do I2S), Timers, USB, Ethernet, GPIO. When I initially looked around for a CPU for this gizmo, the MPC5200 looked like a good choice. Right now, this second alternative is probably what I am going to prototype out and see how it goes. Unfortunately, this consumes an interface just to get the clock into the chip and I have already assigned other tasks to all the serial controllers. Alternately, the MPC5200 does let me input a bitclock on one interface and use it as the master clock to another interface. The MPC5200 does not let me generate a bitclock and frameclock from an external mclock, so, I would have to put the interfaces into slave mode and provide them with bit and frame clocks. It is just mighty convenient to use the internal clock of the MPC5200 and leave the serial interfaces in master mode. I am going to incorporate an external clock. how much error is too much error? I already have about $40 in expensive chips so adding the external audio clock generator would add about 10% to my 'expensive components' pile. It also complicates the design a little more. Adding an audio clock generator to the design might add as much as $4 to the design. I can clock the serial channels of the MPC5200 with an external clock. A 2.31% error on a 192KHz signal means that it is actually running at 187.56KHz. However, the worst is 2.31% error at 192KHz. The best I can do is 0.07% error on a 32KHz signal. So, you can only approximate some of the more important audio frequencies. The problem is that the clock divider on the MPC5200 does not have enough precision. It does not have a very accurate clock generator for audio frequencies. However, it has one serious drawback as an audio processor. Fast, low power, PowerPC, FPU, multiple serial controllers. I am using a Freescale MPC5200 as the CPU in a gizmo I am working on. but if you had a choice of adding to the cost of goods or going with something a little less accurate, what would you do? I am curious about how much clock inaccuracy is acceptable in a pro-audio device.
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