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miniDSP Low cost, modular Digital Signal Processor (DSP) kits for the DIYer from miniDSP.

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Old 28th October 2010, 03:44 AM   #51
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Originally Posted by victor_2 View Post
I think that DSP is more expensive as it will need at least 6 channel volume control (resistive or inductive) and at least 6 channel DAC if our signal source is PCM. In case of DSD it has to be converted to PCM and if the source is a LP or a tape an additional ADC has to be used. I believe the digital approach may be a more transparent solution at least for PCM. But for hi and low pass filters I would still prefer to use FIR filters.
Actually, you don't really need analog-domain volume controls, as shaped dither is quite transparent if it's applied at well over the audible range. Oversampling the signal before dither helps tremendously: I had a 6 bit signal almost indistinguishable from the original when dither/truncation was applied after resampling at 2x.
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Old 2nd November 2010, 11:19 PM   #52
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Originally Posted by DSP_Geek View Post
Actually, you don't really need analog-domain volume controls, as shaped dither is quite transparent if it's applied at well over the audible range. Oversampling the signal before dither helps tremendously: I had a 6 bit signal almost indistinguishable from the original when dither/truncation was applied after resampling at 2x.
I'm not sure about oversampling in this case as it is not going to recover the lost data. Dithering helps to decorelate quantization noise introduced by lowering the resolution of the signal (it converts it essentially into noise), but it will not recover lost bits either.
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Old 3rd November 2010, 12:49 PM   #53
macboy is offline macboy  Canada
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You don't necessarily "lose bits" with DSP processing. I don't know about the Mini-DSP, but in some other DSPs I have used, the internal datapath is so wide that you simply will not "lose bits" due to processing. In the TI TAS3103, the internal datapath is entirely 48 bit. At the output, you can do up to 32 bit with dithering. The incoming audio is packed into the 48 bit input stream with 8 bits for overhead (allowing for gain in your EQ/filters without overflow) and nominally 40 bits for the data. That pushes the noise floor of the DSP to 20 bits (120 dB) below that of 16 bit CD, and there is an extra 48 dB of overhead. The 32 bit dithered output ensures that the noise floor of the digital signal output is well below that of any analog electronics that follow it. If you think you will "lose bits" or resolution with this system (properly used) you are quite mistaken.

Maybe someone who knows the internal details of the Mini-DSP can speak up about its resolution.
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Old 3rd November 2010, 02:25 PM   #54
knuisje is offline knuisje  Netherlands
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From the datasheet of the ADAU1701:

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Most processing is done in full 56-bit, double-precision mode, resulting in very good low level signal performance.
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Old 4th November 2010, 12:11 AM   #55
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I have been optimist in regards to the digital attenuation for level matching between channels. After all I cannot hear any degradation if I use my PC to attenuate signal (ie. headphone listening).

But when I implemented this with MiniDSP, clearly there is audible distortion. I have since put all the attenuation to maximum (0 db) and soldered pots at the output stages to control them analog-ly.

See here:
MiniDSP

Meanwhile, I'm finished my speakers and amps so I will have time soon to continue this learning effort to replicate Orion ASP.
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Old 4th November 2010, 12:45 AM   #56
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Internaly DSP can process the data with any precision. But a the and it has to downsample to number of bits a DAC can accept. And all parts of the output signal where the level is less than Odb some precision will be lost. The magnitude of the loses depends mostly on the level of attenuation of the signal.
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Originally Posted by macboy View Post
You don't necessarily "lose bits" with DSP processing. I don't know about the Mini-DSP, but in some other DSPs I have used, the internal datapath is so wide that you simply will not "lose bits" due to processing. In the TI TAS3103, the internal datapath is entirely 48 bit. At the output, you can do up to 32 bit with dithering. The incoming audio is packed into the 48 bit input stream with 8 bits for overhead (allowing for gain in your EQ/filters without overflow) and nominally 40 bits for the data. That pushes the noise floor of the DSP to 20 bits (120 dB) below that of 16 bit CD, and there is an extra 48 dB of overhead. The 32 bit dithered output ensures that the noise floor of the digital signal output is well below that of any analog electronics that follow it. If you think you will "lose bits" or resolution with this system (properly used) you are quite mistaken.

Maybe someone who knows the internal details of the Mini-DSP can speak up about its resolution.
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Old 6th November 2010, 06:40 PM   #57
Davey is offline Davey  United States
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Originally Posted by gainphile View Post
But when I implemented this with MiniDSP, clearly there is audible distortion. I have since put all the attenuation to maximum (0 db) and soldered pots at the output stages to control them analog-ly.
Do you have any measurements showing said distortion? What input signal levels were you using? Any other details?

Dave.
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Old 7th November 2010, 09:15 PM   #58
cuibono is offline cuibono  United States
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Hi Gainphile - thanks for all this info - it is really encouraging. I'm on a similar path, and it really has its ups and downs...

I'd love to know more about the problem with the digital attenuation, as it looks like such a nice option. I've read your other two threads on it. I wonder if anyone else is having such problems...
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Old 11th November 2010, 12:37 AM   #59
cuibono is offline cuibono  United States
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I've noticed in my system (where I do digital attenuation), it requires a lot of reduction. -40dB-ish. I've also measured an increase in THD with more and more attenuation. Maybe gainphile is really cranking it down?
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Old 11th November 2010, 01:53 AM   #60
Davey is offline Davey  United States
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Tell me how you're measuring that THD increase on your MiniDSP.

I've performed a bunch of distortion tests on my MiniDSP's with varying levels of attenuation using a 10k system volume control and/or with programmed attenuations applied to individual outputs. I don't see any increase in distortion.

Cheers,

Dave.
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