Hello! I have an older DSP that doesn't have a digital input.
I have the schematic for it. The A/D converter is a PCM1802. Fairly certain I've seen digital input boards for a reasonable price. Would it be as simple as disabling/removing the current A/D and connecting power to the converter and connecting the data/LRCK/BCK/MCK and selecting the interface mode?
I have the schematic for it. The A/D converter is a PCM1802. Fairly certain I've seen digital input boards for a reasonable price. Would it be as simple as disabling/removing the current A/D and connecting power to the converter and connecting the data/LRCK/BCK/MCK and selecting the interface mode?
You're trying to do something similar to this activity, for the same good reasons.
Convert CD output from analogue to S/PDIF
I had a headache navigating the I2S, left-justified, right-justified, 16b, 24b, undefined formats, and found a solution that did not need me to get to the bottom of it.
Your thinking and approach is that same that mine was until I found a different solution. Your logic sounds right to me. I wish you better success than I achieved.
I think a module that would do the conversion you need would be the receiver version of this. It turns optical or coax S/PDIF into I2S, and the format can be selected by switches.
S/PDIF to I2S converter on eBay
Convert CD output from analogue to S/PDIF
I had a headache navigating the I2S, left-justified, right-justified, 16b, 24b, undefined formats, and found a solution that did not need me to get to the bottom of it.
Your thinking and approach is that same that mine was until I found a different solution. Your logic sounds right to me. I wish you better success than I achieved.
I think a module that would do the conversion you need would be the receiver version of this. It turns optical or coax S/PDIF into I2S, and the format can be selected by switches.
S/PDIF to I2S converter on eBay
IMO the DSP with ADC has an internal master clock (most likely the ADC running in I2S slave mode), while your SPDIF receiver will by principle be the master itself (as SPDIF carries the clock). Even if the SPDIF receiver could run in slave mode, it would expect that the incoming I2S clocks be synchronous with the master clock the SPDIF receiver generates from the incoming SPDIF stream.
In other words - IMO just replacing the ADC I2S with SPDIF receiver I2S will not work correctly.
Pretty much. I have a very old DSP56002 EVM floating around somewhere with a Crystal Semiconductor codec on it. Replacing the codec with SPDIF i/o would be simple. LEGO make more complicated things. This is ultimately a rules based setup. Understand them and you won't go far wrong. There are posts in the forum where SPDIF and USB I/O have been successfully added. Post the schematic and see where it leads.
I agree with phofman above. When operating with S/PDIF, the DSP must obtain its master clock from the S/PDIF clock. This maybe done by running the DSP from an MCLK output by the clock recovery circuit of the S/PDIF receiver. Alternatively, the XTAL oscillator of the DSP maybe replaced with a PLL frequency multiplier (like the 74HC4046) with its reference input connected to the LRCLK (=fs) or BCK (=64*fs) of the I2S output from the S/PDIF receiver (e.g. STA120).
Phofman's point is also important in the event of a change in the audio sample frequency when the DSP needs to shift its internal clocks accordingly. For example, a 48kHz filter with a cutoff of 1kHz would have a cutoff of only 918.75Hz when run at 44.1kHz.
Hope that helps.
Phofman's point is also important in the event of a change in the audio sample frequency when the DSP needs to shift its internal clocks accordingly. For example, a 48kHz filter with a cutoff of 1kHz would have a cutoff of only 918.75Hz when run at 44.1kHz.
Hope that helps.
I agree. Basically all AV receivers use ASRC on SPDIF/HDMI inputs, otherwise clocking their extensive DSP would be very complicated.