AudioCircle

Industry Circles => Hollis Audio Labs => Topic started by: HAL on 8 Jul 2019, 09:07 pm

Title: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 8 Jul 2019, 09:07 pm

The dspMusik is more than a DSP crossover.

Have been working with one dspMusik customer that has developed a phono preamp that uses the dspMusik for the DSP RIAA EQ along with is digital crossover.   

It is using a commercially available balanced flat gain preamp for the MC cartridge with resistive and capacitive loading.

He has done response measurements that looks very good and now is listening to the results in comparison to his tube phono section.

Hope to hear his results when ready.

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: dpd on 10 Jul 2019, 02:58 am

Here are the measurements of my dspMusik RIAA EQ and SP-9 both actual and error from theoretical.  Gains were normalized to 0.0 dB at 1 KHz.

Magnitude and Phase Response

(https://www.audiocircle.com/image.php?id=196425)


Magnitude and Phase Error

(https://www.audiocircle.com/image.php?id=196426)


dspMusik:

• The low frequency phase error is most likely due to AC coupling on the input of the dspMusik (Rich - can you confirm?), but I believe that to be very negligible.
• The high frequency error is due to warpage of the digital filters (96 KHz Nyquist).  In the critical range, the error is within ~0.16 dB
• NO external circuitry was in the measurement loop - this is from dspMusik Analog Input to its DAC Output (I routed the RIAA EQ filters directly to a DAC output)

SP-9:

• The low frequency phase error is most likely due to AC coupling on the input
• The high frequency error is very minimal due to all analog circuitry.

I think the dspMusik RIAA is quite competitive in response in the critical audio range.  Listening will tell if the HF response error in the dspMusik is audible (to me) or not.  I'm nearly 65, and my hearing most likely will never detect the response errors above 20 KHz.

Some notes:

I calculated the theoretical transfer function response using the 3180 uS, 318 us, and 75 uS time constants used in the RIAA reference response.

Measurements were made with a Keysight EDUX1002G digital oscilloscope using its built-in function generator and transfer function analysis software.  Resolution was 50 pts/decade in a log sweep.  Data was transferred to the spreadsheet for plotting the graphs shown above.[/list]

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: dpd on 10 Jul 2019, 03:20 am

As Rich noted in the OP, I am using a flat gain preamp - a Channel D Lino with fully balanced I/O.

My phono system:

VPI HW-19MkII turntable
Eminent Technology ET-II Air Bearing linear tracking tonearm
Carnegie Madrigal 1 - rebuilt by The SoundSmith
Balanced interconnect to Lino preamp input using Mogami 2534 (quad mic cable)
Balanced interconnect to dspMusik using cables provided by HAL with the dspMusik

Cartridge setup using the original ET-II jig for overhang.  Stylus angle set to ~92 deg using a cheap USB microscope,.  L/R balance (still being adjusted) using an old CBS Test Record with 1 KHz L/R/Mono tones.
[/list]

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 14 Jul 2019, 09:34 pm

dpd,
Very nice RIAA EQ design!  The measurements look very good!

Have a flat gain phono stage in work to give this a try.  Will have cartridge loading and selectable gain for trials with the Shure Ultra 500 cartridge.

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 20 Jul 2019, 01:45 am

The flat gain phono system will be here next week. 

Will implement the RIAA EQ in The Monoliths dspMusikLCD block diagram and get it ready for trials once the system arrives.

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 27 Jul 2019, 02:21 am

For the RIAA EQ testing with the dspMusik, my DSA Phono One beta unit was modified for flat gain use to drive the ADC for DSP EQ. 

Will be adding the RIAA EQ processing to The Monoliths digital crossover design to do both with the system. 

This will be the first implementation of no linear phase digital RIAA EQ and digital crossover for a system to my knowledge.  Neither the ADC or DAC's are using linear phase filter types.

The listening trials begin tomorrow.

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 27 Jul 2019, 09:56 pm

The DSA Phono One modified for flat response for use with the DSP RIAA EQ in the dspMusikLCD processor running The Monoliths speakers crossover.

The modified Oracle Delphi MKI and SME Series III arm and Shure Ultra 500 cartridge are working and playing vinyl.

Title: Re: Using the dspMusik for DSP RIAA EQ for phono
Post by: HAL on 28 Jul 2019, 12:13 pm

Picture of the Oracle Delphi MKI and DSA Phono One driving the dspMusikLCD 2x8 DSP processor and RIAA EQ.

(https://www.audiocircle.com/image.php?id=197023)