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JIMV
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Upsampling?

I have asked variations of this before bt I am still very confused. I have purchased a used Benchmark DAC1 that specifies 24/192 upsampling. The owners manual does not in any way explain what this means and how it works. I do not mean on the signal but how one has the DAC upsample. Is this an automatic function of some sort? Does it take a data stream from my CD player as transport and automatically upsample to some level and if so, how does it know what to upsample to. There are no controls or switches on the unit associated with upsampling.

Please forgive the repitition but I still do not knw hw this works and figure somene out there must own one and know.
?????

RGibran
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Re: Upsampling?

Curious where you have seen this specified? I am unaware the DAC1 upsamples, except for the USB model which I believe upsamples the USB feed to 24 bits. Otherwise the unit *supports* up to 24/192 if fed such signals.

RG

Editor
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Re: Upsampling?


Quote:
I have purchased a used Benchmark DAC1 that specifies 24/192 upsampling. The owners manual does not in any way explain what this means and how it works.

The DAC chip in the Benchmark runs at a constant 100kHz, which is the sample rate at which it performs best. A sample-rate-converter chip upstream of the DAC converts whatever sample-rate material you feed the Benchmark to 100kHz-sampled data. An additional benefit of doing this is that the DAC is shielded from jitter in the incoming datastream.

John Atkinson
Editor, Stereophile

JIMV
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Re: Upsampling?

How could it get such a signal from a transport if all it gets is bits?

JIMV
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Re: Upsampling?


Quote:

Quote:
I have purchased a used Benchmark DAC1 that specifies 24/192 upsampling. The owners manual does not in any way explain what this means and how it works.

The DAC chip in the Benchmark runs at a constant 100kHz, which is the sample rate at which it performs best. A sample-rate-converter chip upstream of the DAC converts whatever sample-rate material you feed the Benchmark to 100kHz-sampled data. An additional benefit of doing this is that the DAC is shielded from jitter in the incoming datastream.

John Atkinson
Editor, Stereophile

So, if I understand you, and I may very well not, the data stream from my CD player's digital out will be upsampled as necessary to 100khz. In explaining this please speak in baby talk as I am not any sort of a tech. I operate in the , plug in all the cables and forget the thing mode. If anything happens variable beyond that and there is not a switch on the machine activating it, I do not understand it.

I guess I was expecting something like a polarity change switch requiring me to do something to get the best sounding polarity. This sounds like any change is automatic as long as I use the Toslink conection.

scottgardner
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Re: Upsampling?

Maybe a few definitions are in order: (mine simplified)

Sampling: Create digital stream by slicing incoming analog signal into varying (amplitude) bit-length pieces. How many of these slices you get per second is the sample-rate: 48k, 96k, 192k... The bit-depth 16, 24... comes from the varying bit-length.

This is done in an ADC (Analog to Digital Converter).

Upsampling: Take a digital stream that is at one sample-rate and bit-depth and create more slices (higher sample-rate) at a finer bit resolution (more bits = greater bit-depth).

This can happen anywhere a designer sees fit to do it.

A DAC will automatically adjust to an incoming digital sample-rate/bit-depth up to its internal capability.

Usually what happens is that the CD reads the bits off the disk at some sample-rate and bit-depth and passes that on to a DAC that then adjusts itself to the incoming stream and then does its Digital to Analog Conversion.

Some DAC's will upsample prior to Conversion to Analog.

mrlowry
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Re: Upsampling?

CD data is 16 bits at 44.1 kHz. What this means in plain English is that each second is divided into 44,100 slices of data, think of them as columns. The column has 16 rows that either have a 1 or 0 in them (on or off.) What I think that Scott is saying is that the Benchmark works at 100kHz so that there are 100,000 columns instead of the standard 44,100. The DAC does "the math" and translates (or upsamples) the 44,100 columns of incoming data into 100,000 columns of data.

scottgardner
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Re: Upsampling?

Yes, that's a great way to see it. If you can visualize a grid being placed over a wave of music that would be sampling. If you then overlay another grid that has smaller cells, you have upsampling. Downsampling would just the opposite.

100K is John's number. I don't have specifics on the DAC1. The 100k brings up an interesting question, however, but probably should be avoided at this point.

JIMV
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Re: Upsampling?

Thank you both as that is understandable to me. What about the word size...16 o 24?

scottgardner
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Re: Upsampling?

Word size = bit depth.

Have a look at this: http://www.musiciansfriend.com/document?doc_id=88273&src=3SOSWXXA

It goes into better detail and has illustrations that match our explanations.

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Re: Upsampling?


Quote:
Thank you both as that is understandable to me. What about the word size...16 o 24?

The data on the CD are described as 16-bit words, which covers 65,536 signal levels. Any time you apply processing to a digital datatstream, you increase the length of the words. In the case of the DAC chip used by the Benchmark, it accepts 24-bit data, so I assume that the data coming from the sample-rate converter chip are 24-bit words, which can describe 16,777,216 signal levels.

Even so, the sample-rate conversion does not add resolution that wasn't preserved in the CD's data, only that the use of 24-bit data presented to the DAC chip maximizes the mathematical precision of the conversion.

John Atkinson
Editor, Stereophile

JIMV
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Re: Upsampling?

Thanks

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