Audio-Next : True 768Khz 32 bits of SPDIF/I2S/Dop/DSD/SRC/ASRC !! - diyAudio
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Old 2nd December 2015, 07:56 AM   #1
kfshu2 is offline kfshu2  Taiwan
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Default Audio-Next : True 768Khz 32 bits of SPDIF/I2S/Dop/DSD/SRC/ASRC !!

True 32 bits of SPDIF 768khz :


ComTrue Inc. - Products

.SPDIF 768k/32
.PCM 768k/32
.DSD 8x
.Dop 4x
.ASRC/SRC
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Old 2nd December 2015, 09:23 AM   #2
Zoran is offline Zoran  Serbia
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Location: Belgrade
thanks
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Old 3rd December 2015, 03:38 PM   #3
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Do you know if it supports +0dBFS signals? (intersample peaks over 0dBFS)
Hi-end DSP based multi-channel integrated Preamp/Crossover/DAC project
I see you have the ASRC before the volume control.

Maybe thre will be inexpensive digital volum and samplerate controls now, for us that is not affraid of digital attunation but want to do it outside the PC.

Regards Torgeir
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Old 3rd December 2015, 05:34 PM   #4
kfshu2 is offline kfshu2  Taiwan
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Quote:
Originally Posted by torgeirs View Post
Do you know if it supports +0dBFS signals? (intersample peaks over 0dBFS)
Hi-end DSP based multi-channel integrated Preamp/Crossover/DAC project
I see you have the ASRC before the volume control.

Maybe thre will be inexpensive digital volum and samplerate controls now, for us that is not affraid of digital attunation but want to do it outside the PC.

Regards Torgeir
input signal range = 0x7fff_ffff ~ 0x8000_0000 (sign)

ASRC = 3-stage FIR filter with 64-bit resolution, 0.5 LSB distortion

volume control = +18dB ~ -110dB step 1/32 dB

output signal range = 0x7fff_ffff ~ 0x8000_0000 (sign)



In this case input=sign 32-bit, FIR=sign 64-bit, volume=sign 32-bit,
distortion=0.5 LSB,

and we can get 31.5 bits accuracy.



: I think Ur question is interpolation filter & re-sample issue.


as I know, answer is yes. This chip, CT7302PL, can maintain +0dBFS.
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Old 3rd December 2015, 08:05 PM   #5
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Quote:
Originally Posted by kfshu2 View Post
input signal range = 0x7fff_ffff ~ 0x8000_0000 (sign)

output signal range = 0x7fff_ffff ~ 0x8000_0000 (sign)



: I think Ur question is interpolation filter & re-sample issue.


as I know, answer is yes. This chip, CT7302PL, can maintain +0dBFS.
I dont understand how it can handle intersample overload without having higher output signal range than input signal range. My bet is 4 bit resolution and noise at -20dBfs
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Old 3rd December 2015, 08:38 PM   #6
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As stated the problem is that a signal with intersample overloads should be attunated the same amount as the intersample overload max.
Normaly -6dB would do the trick.
I guess two chips in series would solve it:
The first has no SRC been done only -6dB attunation -> Transfer samples at 32 bit -> The second has SCR or ASRC and then digital volum control.
After digital volum control there should be no need for signals at more then -6dBFS with a high quality DAC and propper analog gain before the amps.
If it is a digital amp fed intersample overloaded signals it will clipp them.

Regards Torgeir
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Old 4th December 2015, 01:44 AM   #7
kfshu2 is offline kfshu2  Taiwan
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Join Date: Oct 2014
Quote:
Originally Posted by torgeirs View Post
I dont understand how it can handle intersample overload without having higher output signal range than input signal range. My bet is 4 bit resolution and noise at -20dBfs

for example :

sample rate = 48khz, single tone

if : input signal = 12khz sin tone, 2pi/4 offset

=>0dB max = 0x7fff_ffff



if : input signal = 12khz sin tone, 2pi/8 offset

=>0dB max = 0x7fff_ffff * sin(2pi/8)



: u may think about frequency domain, not time domain.

not all 0dB max value = numeric max value
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Old 4th December 2015, 08:18 AM   #8
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I am thinking about the signal enclosed in the posts:
Hi-end DSP based multi-channel integrated Preamp/Crossover/DAC project
or
Software to detect +0dBFS waveforms and overload times

In your example you have to resample upwards. Then calculate again.
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Old 4th December 2015, 08:41 AM   #9
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BTW, I really like your product if it lives up to the spec!

And to the non believers in digital volum control bacause of noise
Point 1:
Vn=√(4*Kb*T*R* Δf) (V)
Thermal noise of resistor - Calculator - Audio PerfectionAudio Perfection
Dynamic range re 3V RMS = 144.4 dB for 100ohm
Dynamic range re 3V RMS = 134.4 dB for 1000ohm
Dynamic range re 3V RMS = 124.4 dB for 10k
Dynamic range re 3V RMS = 117.6 dB for 47k

Point 2:
DAC from PCM1798 | Audio DAC | Audio Converters | Online datasheet
Distortion from -10 to 0 dBFS is almost the same relativ to signal.
Click the image to open in full size.

So source impedance or analog feedback resistors in buffers and analog volum control must be pretty low to gain any advantage from analog volume control.
A firm like RME has abandoned it.

Last edited by torgeirs; 4th December 2015 at 09:03 AM.
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Old 4th December 2015, 09:12 AM   #10
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(I use analog volum control only because I have not found a reliable digital one yet. I mean one that don't say pop/bang or ssssssss at high volume during fault conditions)
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