Minidsp Flex Review (Audio DSP)

[Ultrasonic]

The eq is not the problem here. The phono cartridge just has to little output for a normal line level I put. It needs massive amplification before it’s usable.

^This. Plus I think possibly an input impedance issue too?

The way to no longer need a phono preamp is to no longer play vinyl...

 

[Pdxwayne]

No, I need a citation for the claim that it can't do 44.1kHz.

Most stuff that says 48kHz really means "44.1 or 48".

(Do you think it can't do 48kHz unless you have Dirac Live?)

It would be great if @amirm can also measure performance for 44.1. All his measurements are in 48, 96, etc, as far as I noticed.

 

[mdsimon2]

No, I need a citation for the claim that it can't do 44.1kHz.

Most stuff that says 48kHz really means "44.1 or 48".

(Do you think it can't do 48kHz unless you have Dirac Live?)

It can accept a wide variety of input sample rates but it will ASRC that sample rate to the internal rate of 96 kHz (2X4HD plugin) or 48 kHz (DDRC-24 plugin).

It would be great if @amirm can also measure performance for 44.1. All his measurements are in 48, 96, etc, as far as I noticed.

Dashboard is run at 44.1 kHz.

Michael

 

[mdsimon2]

I understand on the TRS version, if an analog input used of TRS-RCA will degrade the sound (don't have an issue as I am not using this, will plan to use the USB input).

But what about using TRS to RCA on the output, is the same degraded performance will be applied?

@amirm any chance we can get a digital input measurement using a TRS to RCA cable on the output?

Michael

 

[JDubya]

Well, not so fast. The thing still only has 16-bit equivalent performance despite the 110+ SINAD, and word on the street is the second pair of channels is significantly worse. It almost looks like companies also know that Amir only measures the first set of channels

Apologies for the newbie question but could you or Amir please elaborate on the 16-bit equivalent performance?

Is this only with respect to the ADC conversion when using the analog inputs, or is this with respect to all DAC performance? If the latter, does this mean the audio benefits of 24 bit digital inputs won't be realized - such that it's not really high performance for hires (24bit) audio?

The unit measures well so I'm struggling to understand the practical implications of this issue for 24 bit audio. Thanks!

 

[Jaimo]

^This. Plus I think possibly an input impedance issue too?

The way to no longer need a phono preamp is to no longer play vinyl...

I have no issues with either sourcing or building an instrumentation grade linear amplifier for gain and impedance matching. The bigger issue is building a good analog equalizer. EQ is a thing for the digital domain.

So, is there a phono EQ plug-in that will work with Mini-DSP?


Edit: Should have googled first…

Just found this…https://www.minidsp.com/support/forum/hometheater-av-applications/12510-2x4-hd-as-phono-preamp

 

[Ultrasonic]

So, is there a phono EQ plug-in that will work with Mini-DSP?

MiniDSP sell no software targeted at doing what you are asking for, and their advice is generally to use a good phono pre-amp. I don't know whether it would be technically possible to manually implement the required EQ using the PEQ/FIR functionality though.

 

[Pdxwayne]

It can accept a wide variety of input sample rates but it will ASRC that sample rate to the internal rate of 96 kHz (2X4HD plugin) or 48 kHz (DDRC-24 plugin).

View attachment 186106



Dashboard is run at 44.1 kHz.

Michael

Oh, my mistake. Need to enlarge to see in my phone's screen. Thanks!

Do you know what is the bit rate? 16, 24, etc?

I noticed something odd with my gustard x16 high hat tone when sending 16bit vs 24bit from my Windows laptop using Audio advanced setting.

 

[abdo123]

@Ultrasonic @Jaimo @voodooless

The flex is easily capable of 40dB gain needed for phono inputs, I've done it before.

For some reason it didn't sound right, perhaps some impedance interaction with my cartidage. With the cambridge phono duo the line output occasionally goes above 2vrms so it's also something to keep in mind.

 

[buz]

Impressive.

Not entirely comparable but still very interested to see what the qudelix t71 will bring in terms of multi channel DSP

 

[abdo123]

@Jaimo There is a community effort that produced the filters necessary for RIAA EQ in FIR format. Should be very easy to copy into the application.

 

[Ultrasonic]

@Ultrasonic @Jaimo @voodooless

The flex is easily capable of 40dB gain needed for phono inputs, I've done it before.

For some reason it didn't sound right, perhaps some impedance interaction with my cartidage. With the cambridge phono duo the line output occasionally goes above 2vrms so it's also something to keep in mind.

The issue with trying to use such large gains would likely be audibility if the noise floor I'd have thought, as was mentioned above. Noting the reduced measured performance in the analogue inputs too.

I've never bought any records in my life though and have zero intention of ever doing so. Others are therefore far better informed to comment on this subject than me .

 

[mdsimon2]

Oh, my mistake. Need to enlarge to see in my phone's screen. Thanks!

Do you know what is the bit rate? 16, 24, etc?

I noticed something odd with my gustard x16 high hat tone when sending 16bit vs 24bit from my Windows laptop using Audio advanced setting.

It operates at 32 bit internally.

I’m a bit of a curmudgeon but I hate windows audio, too difficult to tell what is going on.

Michael

 

[voodooless]

@Ultrasonic @Jaimo @voodooless

The flex is easily capable of 40dB gain needed for phono inputs, I've done it before.

That is quite impressive if there is still no noise after 40dB!

For some reason it didn't sound right, perhaps some impedance interaction with my cartidage.

Well yes, you need proper matching with the cartridge as well, especially capacitance.

 

[KMO]

It can accept a wide variety of input sample rates but it will ASRC that sample rate to the internal rate of 96 kHz (2X4HD plugin) or 48 kHz (DDRC-24 plugin).

Okay, seems like it does indeed not directly process 44.1kHz-based signals. I found someone having a closer look at the SRC of an earlier-gen product:

Measurements of MiniDSP 2x4HD

@BE718 Well I get the same results with Audacity and Wave Spectra. Here are some measures of an actual device. The cyan line is an 18i20 which is running 77 ppm fast. The gold line is the same signal once the speed has been corrected within about 10 ppb more or less. The second image has a...

audiosciencereview.com

Artefacts down at the -130dB level, if I'm reading correctly.

 

[voodooless]

Apologies for the newbie question but could you or Amir please elaborate on the 16-bit equivalent performance?

Look at the multitone measurements. There the noise is at roughly -96 dB, so about 16 bits. Everything below is noise and intermodulation products. So we here have a device that can play one tone very well (18 to 19 bits equivalent), but when it comes to music, it only retains about 16 bits.

Is this only with respect to the ADC conversion when using the analog inputs, or is this with respect to all DAC performance?

It’s purely the DAC performance.

If the latter, does this mean the audio benefits of 24 bit digital inputs won't be realized - such that it's not really high performance for hires (24bit) audio?

I would not worry to much about that. You most likely won’t hear the difference anyway. 16 bits is still plenty, just not state of art.

 

[anotherhobby]

Okay, seems like it does indeed not directly process 44.1kHz-based signals. I found someone having a closer look at the SRC of an earlier-gen product:

Measurements of MiniDSP 2x4HD

@BE718 Well I get the same results with Audacity and Wave Spectra. Here are some measures of an actual device. The cyan line is an 18i20 which is running 77 ppm fast. The gold line is the same signal once the speed has been corrected within about 10 ppb more or less. The second image has a...

audiosciencereview.com

Artefacts down at the -130dB level, if I'm reading correctly.

Interesting! I don't know if we can expect the Flex to behave exactly the same as the 2x4HD, but it's possible.

My only source is my Mac, and I configured Audio MIDI Setup so the Mac outputs 48 kHz. I figured this was likely the best way to set it up since CoreAudio does a very good job of resampling, and Dirac operates at 48 kHz. If I configure the Mac to other rates I can't tell any difference, so I don't know how valid my line of thinking is, but if the Flex behaves like the 2x4HD, then it looks like I'm set up for the better.

 

[NTK]

This does help…. Another question,

Is it possible to route the analog input to a digital RIAA equalizer and be rid of old school phono equalizers?

Assuming you already have the device to amplify cartridge output to line level suitable for input into the MiniDSP, you should be able to use the RIAA EQ biquad coefficients given in MiniDSP's biquad filter spreadsheet.

Refer to this page, go down to the bottom of page, in the "Where to start?" section there is a link to the biquad filter spreadsheet. Open the spreadsheet, and the sheet for RIAA is the next to last sheet.

Advanced Biquad Programming

Flexibility really matters when it comes to innovative speaker design. As DIYers and speaker designers ourselves, we came to realize that miniDSP platforms could be used for both basic and advanced digital signal processing applications. While textbook filter implementation like Butterworth...

www.minidsp.com

Disclaimer: I don't have a miniDSP unit to test, so I don't know if it works. I'd recommend running a frequency response test to see verify that it provides the correct response.

 

[Jaimo]

The issue with trying to use such large gains would likely be audibility if the noise floor I'd have thought, as was mentioned above. Noting the reduced measured performance in the analogue inputs too.

I've never bought any records in my life though and have zero intention of ever doing so. Others are therefore far better informed to comment on this subject than me .

@abdo123 - I'm going to investigate using the FIR filters and a high gain amplifier. I already have a good step up transformer from Softone Japan so this may suffice.

@Ultrasonic I started collecting vinyl in the early 70's and still have a large (2000+) LP collection, many of which I can't find in digital formats. I would like to be able to listen to an occasional LP and introduce the kids to some long forgotten bands.

The Mini-DSP unit looks like a workable option for me.

 

[Ultrasonic]

@Ultrasonic I started collecting vinyl in the early 70's and still have a large (2000+) LP collection, many of which I can't find in digital formats. I would like to be able to listen to an occasional LP and introduce the kids to some long forgotten bands.

Yes, I totally get why vinyl is still an important source for many. I was just making my lack of experience in this area clear .