recording 16bit (samplitude) with 20bit-converters

[Imre Csonka]

Hello guys

I´m going to record a live concert tomorrow.
I´m recording 32 tracks on a computer with Samplitude and for security 4
ADATs. As far as I know these ADATs got 20bit A/D converters. I´m planning
to take the ADATs optical outputs to get into the computer via a Creamware
Pulsar2 card. However I want to record on Samplitude with just 16 bit depth
due to the limited harddiskspace on my computer.
So here is my question:
Does Samplitude automatically know which Bits to take (the Most Significant
Bits) or have I to level the ADATs analog input signal so that the maximum
level doesn´t exceed the threshold of the 16th bit?

Thank you.

Imre Csonka

[Arny Krueger]

"Imre Csonka" > wrote in message
t
> Hello guys
>
> I´m going to record a live concert tomorrow.
> I´m recording 32 tracks on a computer with Samplitude and for
> security 4 ADATs. As far as I know these ADATs got 20bit A/D
> converters. I´m planning to take the ADATs optical outputs to get
> into the computer via a Creamware Pulsar2 card. However I want to
> record on Samplitude with just 16 bit depth due to the limited
> harddiskspace on my computer. So here is my question:

> Does Samplitude automatically know which Bits to take (the Most
> Significant Bits) or have I to level the ADATs analog input signal so
> that the maximum level doesn´t exceed the threshold of the 16th bit?

When a ADC creates a data word no matter how many bits are in the word, the
word always sums up to full scale which you might think of as being 1.000.
That means that a 16 bit ADC puts out a maximum value of 1.000, and so does
a 20 bit or even 24 bit ADC.

If one ADC has more bits than another, the additional bits are always placed
at the right or low order end. Therefore the rightmost bit has a smaller
value and the ADC can be said to have higher resolution.

This means that its always safe for software to record the high order bits,
no matter how many bits are provided and no matter how many bits are
recorded. You might think of this as Samplitude "knowing" to take the most
significant bits. You can record signals at any level within the analog
specs of the ADC, regardless of how many bits are in a data word. You never
have to cut back on the analog signal because the program is recording fewer
bits than the maximum that the ADC can deliver.

There are some more subtle things that happen when you arbitrarily strip off
low-order bits. This relates to dither, which is a whole 'nuther topic.

[Mike Rivers]

In article > writes:

> I´m recording 32 tracks on a computer with Samplitude and for security 4
> ADATs. As far as I know these ADATs got 20bit A/D converters. I´m planning
> to take the ADATs optical outputs to get into the computer via a Creamware
> Pulsar2 card. However I want to record on Samplitude with just 16 bit depth
> due to the limited harddiskspace on my computer.
> So here is my question:
> Does Samplitude automatically know which Bits to take (the Most Significant
> Bits) or have I to level the ADATs analog input signal so that the maximum
> level doesn´t exceed the threshold of the 16th bit?

No, and no. What will happen is the 20-bit data will be truncated when
it gets shoved through the 16-bit pipe to the computer. It probably
won't be terribly serious, but it won't be as good as dithering before
truncation (which you can't do with what you have) and it won't be as
good as recording the full resolution.

Are you sure you can't free up more disk space? That would save you a
lot of doubt.

--
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