DSP Measurements and Rising Noise Floor

[spalmgre]

Neurocrome Modulus has been tested at ACR so we know what that represents. Modulus is in my opinion too expensive or let's say that I can not see the added value over a done right version that somebody else has done.

The "Doner right" and several other boards can also work well as there is a lot of good information to find how to develop a working amplifier using the LM3886 chip. Here is a non-China board by Eltim.

I did ask Connex Electronics are their board using genuine chips and quality parts.
This was their answer:
"Hi, We buy parts from reputable suppliers, and up to this date we haven't had issues with LM3886 ICs. The fact that is genuine or not has little to do with noise but a lot more with reliability. Fake chip will undeliver, and possibly blow up when reach the rated power. Probably noisy, but I haven't tried one yet."

I did not buy their LM3886SMPS at that time that I got their answer in 2020. But now I have ordered as they do sell the board without the LM3886 and I have found genuine such to fit myself. This adds up one of the cheapest solutions to get a amplifier that might fill my need for low noise level with my speakers.

 

[mdsimon2]

As a result of this thread Tony from miniDSP reached out to me unprompted and gave me an updated firmware for the 2x4HD to test out.

This firmware implemented two improvements: 1) changed the gain structure so volume control acts before ASRC meaning you can use attenuation in the miniDSP to eliminate intersample over clipping and 2) modified IIR assembly code to improve performance with low frequency EQ. As I understand similar firmware improvements are available for the Flex/SHD/DDRC-24 platforms.

Starting with sending a +3 dBFS 11.025 kHz tone to the miniDSP without volume control. At 0 dB volume position we see intersample over clipping as expected.

However with the new firmware at a volume control position of -3 dB you no longer get clipping.

-0 dB: Input RMS 1.09 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -35.6 dB [20..22000 Hz], THD+N: -35.6 dB [20..22000 Hz]
-3 dB: Input RMS -0.27 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -125.0 dB [20..22000 Hz], THD+N: -125.0 dB [20..22000 Hz]

Testing the applied filters shows some decent improvement across the board.

Sub - 2x4HD - 10 dB noise improvement with new firmware

Base OLD: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS,THD: -145.9 dB based on 49 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Sub OLD: Input RMS -7.33 dBFS, THD: -123.6 dB based on 49 harmonics [20..22000 Hz], N: -108.0 dB [20..22000 Hz], THD+N: -107.9 dB [20..22000 Hz]
Sub NEW: Input RMS -7.33 dBFS, THD: -135.5 dB based on 49 harmonics [20..22000 Hz], N: -118.2 dB [20..22000 Hz], THD+N: -118.2 dB [20..22000 Hz]

Low - 2x4HD - 13 dB noise improvement with new firmware

Base OLD: Input RMS -1.03 dBFS, THD: -145.6 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Low OLD: Input RMS -5.38 dBFS, THD: -143.7 dB based on 49 harmonics [20..22000 Hz], N: -102.9 dB [20..22000 Hz], THD+N: -102.9 dB [20..22000 Hz]
Low NEW: Input RMS -5.39 dBFS, THD: -149.1 dB based on 49 harmonics [20..22000 Hz], N: -115.7 dB [20..22000 Hz], THD+N: -115.7 dB [20..22000 Hz]

High - 2x4HD

Base OLD: Input RMS -1.01 dBFS, THD: -145.8 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.01 dBFS, THD: -146.5 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
High OLD: Input RMS -10.75 dBFS, THD: -144.1 dB based on 21 harmonics [20..22000 Hz], N: -121.8 dB [20..22000 Hz], THD+N: -121.8 dB [20..22000 Hz]
High NEW: Input RMS -10.75 dBFS, THD: -143.3 dB based on 21 harmonics [20..22000 Hz], N: -121.9 dB [20..22000 Hz],THD+N: -121.9 dB [20..22000 Hz]

2x4HD FW 1.6 - Sub - 30 Hz

2x4HD FW 1.6 - Low - 100 Hz

2x4HD FW 1.6 - High - 1 kHz

Overall some really nice improvements in performance and love that they reached out and fixed this issue unprompted.

Michael

 

[mdsimon2]

Updated summary table.

Michael

 

[GWolfman]

Question is @mdsimon2, do you like your LXmini?

I heard one version in person once (had the two dual-woofer subs) and it had a very interesting sound the seemed to fill the entire room. I wanted to listen more but wasn’t able to make it back.

 

[GWolfman]

As a result of this thread Tony from miniDSP reached out to me unprompted and gave me an updated firmware for the 2x4HD to test out.

This firmware implemented two improvements: 1) changed the gain structure so volume control acts before ASRC meaning you can use attenuation in the miniDSP to eliminate intersample over clipping and 2) modified IIR assembly code to improve performance with low frequency EQ. As I understand similar firmware improvements are available for the Flex/SHD/DDRC-24 platforms.

Starting with sending a +3 dBFS 11.025 kHz tone to the miniDSP without volume control. At 0 dB volume position we see intersample over clipping as expected.
View attachment 274143

However with the new firmware if you add 3 dB of attenuation you no longer get clipping.
View attachment 274144

-0 dB: Input RMS 1.09 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -35.6 dB [20..22000 Hz], THD+N: -35.6 dB [20..22000 Hz]
-3 dB: Input RMS -0.27 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -125.0 dB [20..22000 Hz], THD+N: -125.0 dB [20..22000 Hz]

Testing the applied filters shows some decent improvement across the board.

Sub - 2x4HD - 10 dB noise improvement with new firmware
View attachment 274157
View attachment 274152

Base OLD: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS,THD: -145.9 dB based on 49 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Sub OLD: Input RMS -7.33 dBFS, THD: -123.6 dB based on 49 harmonics [20..22000 Hz], N: -108.0 dB [20..22000 Hz], THD+N: -107.9 dB [20..22000 Hz]
Sub NEW: Input RMS -7.33 dBFS, THD: -135.5 dB based on 49 harmonics [20..22000 Hz], N: -118.2 dB [20..22000 Hz], THD+N: -118.2 dB [20..22000 Hz]

Low - 2x4HD - 13 dB noise improvement with new firmware
View attachment 274158
View attachment 274159

Base OLD: Input RMS -1.03 dBFS, THD: -145.6 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Low OLD: Input RMS -5.38 dBFS, THD: -143.7 dB based on 49 harmonics [20..22000 Hz], N: -102.9 dB [20..22000 Hz], THD+N: -102.9 dB [20..22000 Hz]
Low NEW: Input RMS -5.39 dBFS, THD: -149.1 dB based on 49 harmonics [20..22000 Hz], N: -115.7 dB [20..22000 Hz], THD+N: -115.7 dB [20..22000 Hz]

High - 2x4HD
View attachment 274160
View attachment 274161

Base OLD: Input RMS -1.01 dBFS, THD: -145.8 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.01 dBFS, THD: -146.5 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
High OLD: Input RMS -10.75 dBFS, THD: -144.1 dB based on 21 harmonics [20..22000 Hz], N: -121.8 dB [20..22000 Hz], THD+N: -121.8 dB [20..22000 Hz]
High NEW: Input RMS -10.75 dBFS, THD: -143.3 dB based on 21 harmonics [20..22000 Hz], N: -121.9 dB [20..22000 Hz],THD+N: -121.9 dB [20..22000 Hz]

2x4HD FW 1.6 - Sub - 30 Hz
View attachment 274163
View attachment 274164

2x4HD FW 1.6 - Low - 100 Hz
View attachment 274165
View attachment 274166

2x4HD FW 1.6 - High - 1 kHz
View attachment 274167
View attachment 274168

Overall some really nice improvements in performance and love that they reached out and fixed this issue unprompted.

Michael

Fantastic work, thanks!

Still room for miniDSP to improve though (particularly low frequencies).

 

[mdsimon2]

Question is @mdsimon2, do you like your LXmini?

I heard one version in person once (had the two dual-woofer subs) and it had a very interesting sound the seemed to fill the entire room. I wanted to listen more but wasn’t able to make it back.

Yes, I built them in late 2020 and really like them. They are definitely a bit volume limited but I don't listen loud. I wouldn't run them without subs as they become even more volume limited due to the low frequency bass boost that exists in the default EQ.

Overall I think Erin's review is pretty spot on -> https://www.erinsaudiocorner.com/loudspeakers/linkwitz_lx_mini/. They project a large sound stage and sound very natural to me. I think part of it is that they don't look like normal speakers but I've had several people ask if the sound is coming from the TV because they disappear acoustically.

The main A/V source in my living room system is an AppleTV and my wife and I listen to all TV/movies/music with them. I find them exceptionally good at producing clear dialog on movies/TV which is the primary reason they have stuck around in the living room.

They are also the easiest DIY speaker I have ever built, especially if you buy the wood parts from Madisound. Because I like them so much I do plan on building some other speakers with a small full range coupled to a woofer (FAST) with some Scanspeak 10Fs I have laying around but have not got around to it.

Michael

 

[MarcosCh]

As a result of this thread Tony from miniDSP reached out to me unprompted and gave me an updated firmware for the 2x4HD to test out.

This firmware implemented two improvements: 1) changed the gain structure so volume control acts before ASRC meaning you can use attenuation in the miniDSP to eliminate intersample over clipping and 2) modified IIR assembly code to improve performance with low frequency EQ. As I understand similar firmware improvements are available for the Flex/SHD/DDRC-24 platforms.

Starting with sending a +3 dBFS 11.025 kHz tone to the miniDSP without volume control. At 0 dB volume position we see intersample over clipping as expected.
View attachment 274143

However with the new firmware if you add 3 dB of attenuation you no longer get clipping.
View attachment 274144

-0 dB: Input RMS 1.09 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -35.6 dB [20..22000 Hz], THD+N: -35.6 dB [20..22000 Hz]
-3 dB: Input RMS -0.27 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -125.0 dB [20..22000 Hz], THD+N: -125.0 dB [20..22000 Hz]

Testing the applied filters shows some decent improvement across the board.

Sub - 2x4HD - 10 dB noise improvement with new firmware
View attachment 274157
View attachment 274152

Base OLD: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS,THD: -145.9 dB based on 49 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Sub OLD: Input RMS -7.33 dBFS, THD: -123.6 dB based on 49 harmonics [20..22000 Hz], N: -108.0 dB [20..22000 Hz], THD+N: -107.9 dB [20..22000 Hz]
Sub NEW: Input RMS -7.33 dBFS, THD: -135.5 dB based on 49 harmonics [20..22000 Hz], N: -118.2 dB [20..22000 Hz], THD+N: -118.2 dB [20..22000 Hz]

Low - 2x4HD - 13 dB noise improvement with new firmware
View attachment 274158
View attachment 274159

Base OLD: Input RMS -1.03 dBFS, THD: -145.6 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Low OLD: Input RMS -5.38 dBFS, THD: -143.7 dB based on 49 harmonics [20..22000 Hz], N: -102.9 dB [20..22000 Hz], THD+N: -102.9 dB [20..22000 Hz]
Low NEW: Input RMS -5.39 dBFS, THD: -149.1 dB based on 49 harmonics [20..22000 Hz], N: -115.7 dB [20..22000 Hz], THD+N: -115.7 dB [20..22000 Hz]

High - 2x4HD
View attachment 274160
View attachment 274161

Base OLD: Input RMS -1.01 dBFS, THD: -145.8 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.01 dBFS, THD: -146.5 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
High OLD: Input RMS -10.75 dBFS, THD: -144.1 dB based on 21 harmonics [20..22000 Hz], N: -121.8 dB [20..22000 Hz], THD+N: -121.8 dB [20..22000 Hz]
High NEW: Input RMS -10.75 dBFS, THD: -143.3 dB based on 21 harmonics [20..22000 Hz], N: -121.9 dB [20..22000 Hz],THD+N: -121.9 dB [20..22000 Hz]

2x4HD FW 1.6 - Sub - 30 Hz
View attachment 274163
View attachment 274164

2x4HD FW 1.6 - Low - 100 Hz
View attachment 274165
View attachment 274166

2x4HD FW 1.6 - High - 1 kHz
View attachment 274167
View attachment 274168

Overall some really nice improvements in performance and love that they reached out and fixed this issue unprompted.

Michael

Well, i guess the question now is if and when the firmware will be available. I would assume that obviously it will, but did they mention anything regarding that?
Thank you to bring this up and help solving it.

 

[Sokel]

As a result of this thread Tony from miniDSP reached out to me unprompted and gave me an updated firmware for the 2x4HD to test out.

This firmware implemented two improvements: 1) changed the gain structure so volume control acts before ASRC meaning you can use attenuation in the miniDSP to eliminate intersample over clipping and 2) modified IIR assembly code to improve performance with low frequency EQ. As I understand similar firmware improvements are available for the Flex/SHD/DDRC-24 platforms.

Starting with sending a +3 dBFS 11.025 kHz tone to the miniDSP without volume control. At 0 dB volume position we see intersample over clipping as expected.
View attachment 274143

However with the new firmware if you add 3 dB of attenuation you no longer get clipping.
View attachment 274144

-0 dB: Input RMS 1.09 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -35.6 dB [20..22000 Hz], THD+N: -35.6 dB [20..22000 Hz]
-3 dB: Input RMS -0.27 dBFS, THD: N/A based on 0 harmonics [20..22000 Hz], N: -125.0 dB [20..22000 Hz], THD+N: -125.0 dB [20..22000 Hz]

Testing the applied filters shows some decent improvement across the board.

Sub - 2x4HD - 10 dB noise improvement with new firmware
View attachment 274157
View attachment 274152

Base OLD: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS,THD: -145.9 dB based on 49 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Sub OLD: Input RMS -7.33 dBFS, THD: -123.6 dB based on 49 harmonics [20..22000 Hz], N: -108.0 dB [20..22000 Hz], THD+N: -107.9 dB [20..22000 Hz]
Sub NEW: Input RMS -7.33 dBFS, THD: -135.5 dB based on 49 harmonics [20..22000 Hz], N: -118.2 dB [20..22000 Hz], THD+N: -118.2 dB [20..22000 Hz]

Low - 2x4HD - 13 dB noise improvement with new firmware
View attachment 274158
View attachment 274159

Base OLD: Input RMS -1.03 dBFS, THD: -145.6 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Base NEW: Input RMS -1.03 dBFS, THD: -146.3 dB based on 49 harmonics [20..22000 Hz], N: -129.5 dB [20..22000 Hz], THD+N: -129.4 dB [20..22000 Hz]
Low OLD: Input RMS -5.38 dBFS, THD: -143.7 dB based on 49 harmonics [20..22000 Hz], N: -102.9 dB [20..22000 Hz], THD+N: -102.9 dB [20..22000 Hz]
Low NEW: Input RMS -5.39 dBFS, THD: -149.1 dB based on 49 harmonics [20..22000 Hz], N: -115.7 dB [20..22000 Hz], THD+N: -115.7 dB [20..22000 Hz]

High - 2x4HD
View attachment 274160
View attachment 274161

Base OLD: Input RMS -1.01 dBFS, THD: -145.8 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
Base NEW: Input RMS -1.01 dBFS, THD: -146.5 dB based on 21 harmonics [20..22000 Hz], N: -129.6 dB [20..22000 Hz], THD+N: -129.5 dB [20..22000 Hz]
High OLD: Input RMS -10.75 dBFS, THD: -144.1 dB based on 21 harmonics [20..22000 Hz], N: -121.8 dB [20..22000 Hz], THD+N: -121.8 dB [20..22000 Hz]
High NEW: Input RMS -10.75 dBFS, THD: -143.3 dB based on 21 harmonics [20..22000 Hz], N: -121.9 dB [20..22000 Hz],THD+N: -121.9 dB [20..22000 Hz]

2x4HD FW 1.6 - Sub - 30 Hz
View attachment 274163
View attachment 274164

2x4HD FW 1.6 - Low - 100 Hz
View attachment 274165
View attachment 274166

2x4HD FW 1.6 - High - 1 kHz
View attachment 274167
View attachment 274168

Overall some really nice improvements in performance and love that they reached out and fixed this issue unprompted.

Michael

That's really good news!
And I'm glad I was the cause,despite the suspicion my newbie measurements raised at the beginning.

 

[djwkyoto]

This is a really great outcome for your work, thank you so much. Kudos to MiniDSP for reaching out to you, though I wonder why they didn't catch it during their testing.
Really looking forward to the new SHD firmware.

 

[Mnyb]

Stupid question from the peanut gallery here

Firstly, thanks for this tread and further enlightenment about these kinds of product. This whole tread makes an interesting read .

Questions:

Is the mini DSP SHD Studio now an “OK” product to buy with the latest improvements. I have it on my shortlist for future upgrades working as preamp and DAC and DSP .

The latest fixes regarding intersample overs with the ASRC made me question how this thing actually works.
How does the signal chain looks like inside the software ?

In short is the volume control applied before any crossover or eq is applied ? Is this ok ?

Would you not want to run the DSP functions and crossovers on a full scale signal and then apply volume adjustments before the DAC stage ( or in the DAC chip itself).
You still want some input gain adjustments to cope with intersample overs of course .

As it looks from the outside is the volume is applied then you do the crossover and DSP functions ?

I’m a bit miffed that there are errors from the “mathematical functions” actually peaking above the physical noise floor ?
Is it not 2023 would not the whole number crunching be done in 64 bit floating point and we could forget about precision in algorithms altogether. I thought this was a 1990 problem with embedded CPU’s resorting to integer maths

 

[mdsimon2]

Stupid question from the peanut gallery here

Firstly, thanks for this tread and further enlightenment about these kinds of product. This whole tread makes an interesting read .

Questions:

Is the mini DSP SHD Studio now an “OK” product to buy with the latest improvements. I have it on my shortlist for future upgrades working as preamp and DAC and DSP .

The latest fixes regarding intersample overs with the ASRC made me question how this thing actually works.
How does the signal chain looks like inside the software ?

In short is the volume control applied before any crossover or eq is applied ? Is this ok ?

Would you not want to run the DSP functions and crossovers on a full scale signal and then apply volume adjustments before the DAC stage ( or in the DAC chip itself).
You still want some input gain adjustments to cope with intersample overs of course .

As it looks from the outside is the volume is applied then you do the crossover and DSP functions ?

I’m a bit miffed that there are errors from the “mathematical functions” actually peaking above the physical noise floor ?
Is it not 2023 would not the whole number crunching be done in 64 bit floating point and we could forget about precision in algorithms altogether. I thought this was a 1990 problem with embedded CPU’s resorting to integer maths

Personally I don't think the issues observed here were ever of great concern from an audibility perspective.

I haven't tested any of the SHD series but I imagine they have similar issues to the other SHARC based platforms. Maybe someone else can confirm? No additional equipment other than the SHD is required.

Previously it was clear that volume control occurred after the ASRC, but we don't exactly know where in the chain. Now the volume control acts in front of the ASRC. Given all of the SHARC DSPs operate using 32 bit floating point I don't think there will be much difference where the volume control occurs but I can test this by comparing the results of applying attenuation in the miniDSP to the sine sweeps I've already done.

Michael

 

[holbob]

How would somebody apply this attenuation in the dirac based minidsp devices (dirac takes over the input channels)?

 

[mdsimon2]

How would somebody apply this attenuation in the dirac based minidsp devices (dirac takes over the input channels)?

Master volume control.

It seems only the gain structure related to the master volume control changed. Attenuation applied to the input / output channels will still result in intersample over clipping if fed a +3 dB tone with no attenuation applied via the master volume control.

Michael

 

[Mnyb]

Personally I don't think the issues observed here were ever of great concern from an audibility perspective.

I haven't tested any of the SHD series but I imagine they have similar issues to the other SHARC based platforms. Maybe someone else can confirm? No additional equipment other than the SHD is required.

Previously it was clear that volume control occurred after the ASRC, but we don't exactly know where in the chain. Now the volume control acts in front of the ASRC. Given all of the SHARC DSPs operate using 32 bit floating point I don't think there will be much difference where the volume control occurs but I can test this by comparing the results of applying attenuation in the miniDSP to the sine sweeps I've already done.

Michael

Ok my current DSP preamp consist of a Meridian G68J that I’ve used for almost 19 years now it’s probably not better than a mini DSP however it has balanced outputs that was not a feature of the G68 ADV amid tested .
It has five Motorola 56367 processors probably with more artefacts than the sharc platform.

Currently I’m using it digital only ( except for the sub ) with Meridian speakers but I have used the analog outs for a couple of years

 

[little-endian]

The CD Player of course doesn't have any kind of volume control

Anyone got an idea about the CD player?

Some CD-Players such as the Technics (SL-PS740A) allow to attenuate the output level which includes the S/PDIF-output in 1dB steps from -12dB and 0dB, at the latter setting being nicely "bit perfect" which unfortunately isn't guaranteed by all devices either.

Can't say though how good the algorithm is for the gain control. Given the age, it will hardly be based on some super-duper 32-bit floating point and whatnot calculation.

 

[ppp000]

Thanks for your hard work Michael, brilliant topic, was hoping someone will do something like this. I have seen your other topics and made buy diyinhk 8 channel dac + aliexpress sharc dsp as minisharc is hard to get, and what you done is very helpful.
Would be lovely to have ADAU1452/66/67 for comparison how they doing in FIR filtering (is double precision even possible like with IIR?) as they are cheap like $50 boards on aliexpress, flexible - all the settings in sigmastudio, no need for costly JTAG or C programming, many functions can be controlled by external MCU over i2c... just big question for me - how they perform IIR seems impressive, but IIR is not why we get DSP If it can handle FIR, think it would be good alternative to miniSHARC, or even much better product.