ADC / DAC Resolution

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I'm working on DSP project and would like to know the optimal resolution DAC & ADC for sampling music and then reproducing it. I know I should be running 48.1kHz but am unsure about the resolution. The music is coming from an "iPod like source"

Thanks

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The optimal resolution would be infinite! The reality is that resolution is a tradeoff.CD quality is 44.1kHz at 16 bits. That would be a starting point. Now you have to look for suitable codecs/adc/dac that are available and suitable for interfacing to the processor you have chosen. TI, Analog Devices and Cirrus Logic would be a starting point for your search.

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As Kartman says, there is no such thing ( practically speaking at any rate ) as optimal resolution. Infinite resolution sounds like a great idea, but, of course, it would also require infinite memory... which doesn't sound as good.

In the end, the chances of your "iPod-like source" having an effective resolution greater than 16-bit is pretty low -- it seems like a reasonable top end.

Martin Jay McKee

As with most things in engineering, the answer is an unabashed, "It depends."

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Number of bits has to do with distortion and signal to noise ratio. 8 bits is 42dB s/n. Like an AM radio. 10 bits is 54dB. Like FM radio. 16 bits is 90 dB like a CD. But then you run the pwm thru a mpeg compressor and throw everything 20dB below the loudest beep in every 4ms sample, so it isn't noisy anymore, but how do you get away with throwing 90% of the samples away without it being audible?
Pro audio stuff started with 12 bits back in the 70s. (Eventide delays)

Imagecraft compiler user

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bobgardner wrote:
... but how do you get away with throwing 90% of the samples away without it being audible?
Near-redundancies.
Our auditory system can tolerate some missing data and still keep a lot of the information.
In Opus, the Swiss Army Knife of Audio codecs by Jean-Marc Valin and company, search for "energy".

"Dare to be naïve." - Buckminster Fuller

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You could import a high quality recording into Audigy and then re-sample to various bit rates and word sizes. See what you can tolerate with respect to rate and word length.

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One point to remember is that if you are doing any sort of processing on your audio, you will need internal bit widths of at least twice your output width... so for a 16 bit output, you'll need internal 32 bit handling (in most cases).

As others have mentioned, 16/44k1 is default CD rate. 8/8k is default telephone (not mobile, that's coded differently and is a *lot* lower bit rate). For most uses, you can half the sample rate to 22k, or 16k as a mid point - you are almost always better off trading bits for sample rate, so keep the 16 bits if you can. That said - analog broadcast TV used a companded 14 bit 32k signal, and transmitted only the most significant ten of those bits - though that needs a little more coding on the input and output side.

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barnacle wrote:
... so for a 16 bit output, you'll need internal 32 bit handling (in most cases).
The TLV320AIC3262 (Texas Instruments) codec has two 24-bit DSPs (one for ADC, one for DAC).
Some compilers have a 24-bit integer type.
Most intrinsic fixed-point types are 16-bit or 32-bit.

"Dare to be naïve." - Buckminster Fuller

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Thanks guys, I was worried about going 16bit b/c for some reason I though any sort of smooth audio would 20bit+

I just spec'd out my stuff and it looks like I'm running 16bit 2 channel dac at 40kHz & 16bit 6 channel adc at 40kHz. Both using SPI to communicate w/ an AVR atmega32

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Remember the SPI maximum bitrate is half the clock rate.

Your bit budget looks like 8 * 16 * 40kb/s = 640kb/s so you should be able to drive them (assuming there's not too much overhead) but you might have difficulty doing any processing on the audio at that speed.

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Shredder - you would want to make sure you adc/dac is suitable for audio use. The audio stuff is usually cheaper and more suited as opposed to instrumentation grade devices.