| Electronics > Projects, Designs, and Technical Stuff |
| Anyone know of a low cost hardware MP3 decoder?? |
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| Siwastaja:
To get any actual resolution (linearity) out of R2R, the resistor matching needs to be ridiculously good, and the output driver impedance adds in series with the resistors, which is a random variable between about 10 to 50 ohms depending on chip, temperature, etc. This is easily many LSbs worth of error even in a 8-bit system already. So that's why DIY R2R usually provides up to about 5-6 bits, or maybe up to 8 if you do it properly. When you reduce the bit depth, you should definitely use dither when constructing the signals. Dither replaces a horribly-sounding quantization noise with a more pleasant white (or shaped, if you wish) noise. Shouldn't be too computationally intensive. If you still have a bit of extra resources available, you could oversample the output if your integrated DAC has excess data rate available, as well; i.e., generate multiple 12-bit samples from a single 16-bit sample. This being said, 12 bits might be enough even without dither. I guess the lack of output filter is the biggest problem. Even a very simple one (-6dB/oct RC) is better than nothing. |
| amyk:
--- Quote from: coppice on May 09, 2020, 03:11:32 am --- --- Quote from: amyk on May 09, 2020, 03:04:41 am ---You don't even need a 32-bit MCU, the countless cheap Chinese players around at the height of the MP3/"MP4" era were based around a Z80 or 8051 and a bit of hardware assistance (multiplier/MAC). --- End quote --- Those players had an 8051 controlling the user interface, and a single chip MP3 decoder. The 8051 was not involved in the decoding at all. --- End quote --- They have only two ICs, a NAND flash and the SoC itself. Those with an FM radio have one more IC for the radio. |
| coppice:
--- Quote from: amyk on May 11, 2020, 02:20:25 am --- --- Quote from: coppice on May 09, 2020, 03:11:32 am --- --- Quote from: amyk on May 09, 2020, 03:04:41 am ---You don't even need a 32-bit MCU, the countless cheap Chinese players around at the height of the MP3/"MP4" era were based around a Z80 or 8051 and a bit of hardware assistance (multiplier/MAC). --- End quote --- Those players had an 8051 controlling the user interface, and a single chip MP3 decoder. The 8051 was not involved in the decoding at all. --- End quote --- They have only two ICs, a NAND flash and the SoC itself. Those with an FM radio have one more IC for the radio. --- End quote --- Fully integrated SoCs came a bit later. Companies like Actions Semiconductors produced single chip solutions with an 8051 core for the UI, and a hardware MP3 decoder. Later they made chips with an ARM core and a hardware decoder. Finally they made devices with a more powerful ARM, and did the decoding in software. That made the solution more flexible as other codecs were needed. I am not aware of device that integrated an FM radio, but it wouldn't surprise me to find one. I expect they mostly used a separate chip. |
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