Watts Up...?

[Rob Watts]

So in theory at least the Qutest would have the most transparent output stage ?
in theory the less components in the signal chain, in practice though I’m guessing maybe not ?

No it doesn't work like that! It's the components in the direct signal path that is important, and that is the same for all the DACs. The second amp that linearises the OP stage is inside the single DAC global feedback path, so the transparency is defined by the feedback components only. In short, as far as transparency is concerned, all the DACs are equivalent to two resistors and two capacitors, as this is the direct signal path.

 

[The Jester]

interesting …
Thanks ..

 

[miketlse]

It shares the same OP stage as Mojo, a very high speed discrete design with a single global feedback path, and this is pure Class A with 300 ohm loads; since Qutest would never see a load less than 300 ohms (as it is intended to drive amplifier inputs - typically 10k ohms to 47k), so it is correct in describing it as Class A. So with other designs, they too would be Class A with a 300 ohm load or greater. With loads less than 300 and high OP voltage, the OP stage goes into Class AB mode; with Hugo2, TT2 and Dave this is not a problem (unlike conventional Class AB) as crossover distortion is eliminated by the second order analogue noise shaper topology. In simple terms this works by employing another amp that has the only job of making the OP stage linear; together with the first amp this allows the complete elimination of measurable crossover distortion (and all other OP stage related distortions). The OP stage amp is inside the global feedback path, which means that the topology is still simple from the direct signal path POV - this is very important as a simple signal path means better small signal accuracy, giving better perception of detail resolution and depth.

Do owners using qutest to directly drive low impedence headphones cause issues?

 

[jarnopp]

Do owners using qutest to directly drive low impedence headphones cause issues?

Probably to their hearing! No volume control on the Qutest so they would be getting 2 or 3v.

 

[Rob Watts]

Then you will get some small measurable crossover distortion - but if you are driving headphones then you should be using Hugo 2. Qutest was designed to drive amps not headphones!

 

[flyte3333]

Hi @Rob Watts ,

If we are doing parametric EQ in software for headphones (or speaker room correction), then would you recommend we keep the same sample rate but also recommended we add dither?

The most popular software these days does EQ in 64-bit float and lots of us like to use 24-bit TOSlink inputs of your DACs. So there will be bit depth reduction from 64-bit float to 24-bit (I can set output to 24-bit before it goes to the USB to TOSlink converter).

So for this use case would you recommended applying dither in software? To avoid truncation by the software.

Is transients reconstruction affected with your DACs if doing this?

Or the dithering noise will be very low and random/uncorrelated , going from 64-bit float to 24-bit, so shouldn't be an issue ?

 

[kennyb123]

It shares the same OP stage as Mojo, a very high speed discrete design with a single global feedback path, and this is pure Class A with 300 ohm loads; since Qutest would never see a load less than 300 ohms (as it is intended to drive amplifier inputs - typically 10k ohms to 47k), so it is correct in describing it as Class A

A belated thanks for taking the time to respond to my question. Really cool design!

 

[ObjectiveSubjectivist]

Hi @Rob Watts ,

If we are doing parametric EQ in software for headphones (or speaker room correction), then would you recommend we keep the same sample rate but also recommended we add dither?

The most popular software these days does EQ in 64-bit float and lots of us like to use 24-bit TOSlink inputs of your DACs. So there will be bit depth reduction from 64-bit float to 24-bit (I can set output to 24-bit before it goes to the USB to TOSlink converter).

So for this use case would you recommended applying dither in software? To avoid truncation by the software.

Is transients reconstruction affected with your DACs if doing this?

Or the dithering noise will be very low and random/uncorrelated , going from 64-bit float to 24-bit, so shouldn't be an issue ?

In my opinion you should always add dither when dropping bits. Otherwise you are creating quantization noise.
But I'm not an expert by any means so I'm curious what Rob is going to say.

 

[GryphonGuy]

In my opinion you should always add dither when dropping bits. Otherwise you are creating quantization noise.
But I'm not an expert by any means so I'm curious what Rob is going to say.

When shortening the word length (eg, 24 to 16 bits for CD production) I have always dithered. Without dithering in this bit-reduction process, nasty "edgy" sounds can appear at times.

 

[flyte3333]

In my opinion you should always add dither when dropping bits. Otherwise you are creating quantization noise.
But I'm not an expert by any means so I'm curious what Rob is going to say.

Agreed

Especially for all music converted to 64-bit float (common) for software parametric EQ, being bit depth reduction to 24-bit for TOSlink output to Rob Watts DACs.

I think we all know how helpful parametric EQ can be with both headphones and speakers.

It will be a compromise, because we know the ideal would be for Rob's FPGA to handle parametric EQ at PCM705/768kHz rates internally. But this is not an option coming anytime soon it seems. So would be great to have advice from @Rob Watts on good approach.

 

[Rob Watts]

Hi @Rob Watts ,

If we are doing parametric EQ in software for headphones (or speaker room correction), then would you recommend we keep the same sample rate but also recommended we add dither?

The most popular software these days does EQ in 64-bit float and lots of us like to use 24-bit TOSlink inputs of your DACs. So there will be bit depth reduction from 64-bit float to 24-bit (I can set output to 24-bit before it goes to the USB to TOSlink converter).

So for this use case would you recommended applying dither in software? To avoid truncation by the software.

Is transients reconstruction affected with your DACs if doing this?

Or the dithering noise will be very low and random/uncorrelated , going from 64-bit float to 24-bit, so shouldn't be an issue ?

Yes absolutely maintain the sample rate, otherwise SQ will be seriously degraded. That said, currently available EQ has subjective problems - 64 bit floating point is not transparent.

Absolutely you must always dither, but the best approach is noise shaping - but you need to be running at 705/768 for this to be 100% effective. When developing the M scaler, I tried different dithering techniques, plus my truncation noise shaping. I was surprised how much better the 11th order truncation noise shaper was - it gave much better depth perception. On the dithering side, rectangular was the worst, next triangular, but pseudo Gaussian (which is almost pure random noise) was much better - but only half as effective subjectively as the truncation noise shaping. So far the available evidence suggests that transients are not degraded by dither or truncation noise shaping. - not at the levels I use it at, but this is something I am currently looking at.

EQ currently implemented has drawbacks - it's certainly not transparent - and I will have a lot more to say about this soon.

 

[flyte3333]

So far the available evidence suggests that transients are not degraded by dither or truncation noise shaping. - not at the levels I use it at, but this is something I am currently looking at.

EQ currently implemented has drawbacks - it's certainly not transparent - and I will have a lot more to say about this soon.

Cheers! Looking forward to hearing more about this in future.

As you can see from others comments and their 'likes' above, other EQ users are interested too.

The ideal way to solve this would be for a Chord app that features parametric EQ to communicate with the DAC FPGA (or M-Scaler) and the EQ itself done inside the FPGA itself not in the app. The EQ is set via an app.

But I don't know if anything like this is even remotely on the radar.

 

[548184]

Hi @Rob Watts,

Important question first. Have you ever been Asha's (Indian Restaurant) for Chicken Tikka Masala (UKs national dish)?

https://news.sky.com/story/amp/tom-...nd-orders-chicken-tikka-masala-twice-12388599

I'm craving for some authentic CTM. Sorry, pandemic talking...

Second question. I run exclusively from RCA out from my Hugo2 for IEM use. If I downgrade to Hugo1, do I still retain this option? What about if I upgrade to a TT2 or DAVE? Since there's no resistor on RCA, only on 6.3mm and 3.5mm, would this overpower my IEMs? I'm phasing out 6.3mm and going exclusively WBT RCA going forward, so trying to decide the next step or to just wait for the Hugo3.

Also, because of supply shortages you may not be able to find your standard battery pack w/ DC available so this might be another option. I believe it has adjustable DC voltage (not just adjust fixed, but user-defined adjust):



https://www.indiegogo.com/projects/storm-2-ultimate-power-mecha-for-digital-nomads#/

 

[Rob Watts]

Hi @Rob Watts,

Important question first. Have you ever been Asha's (Indian Restaurant) for Chicken Tikka Masala (UKs national dish)?



https://news.sky.com/story/amp/tom-...nd-orders-chicken-tikka-masala-twice-12388599

I'm craving for some authentic CTM. Sorry, pandemic talking...

Second question. I run exclusively from RCA out from my Hugo2 for IEM use. If I downgrade to Hugo1, do I still retain this option? What about if I upgrade to a TT2 or DAVE? Since there's no resistor on RCA, only on 6.3mm and 3.5mm, would this overpower my IEMs? I'm phasing out 6.3mm and going exclusively WBT RCA going forward, so trying to decide the next step or to just wait for the Hugo3.









Also, because of supply shortages you may not be able to find your standard battery pack w/ DC available so this might be another option. I believe it has adjustable DC voltage (not just adjust fixed, but user-defined adjust):



https://www.indiegogo.com/projects/storm-2-ultimate-power-mecha-for-digital-nomads#/

Your first question - no not been there. But the best dinner I have ever had was in Bangkok at Gaggon - a 25 course Indian fusion. Absolutely unforgettable.

Second question - all of the DACs have RCA phono wired direct to the headphone contacts - they are all the same, wired from the same OPs.

 

[548184]

Your first question - no not been there. But the best dinner I have ever had was in Bangkok at Gaggon - a 25 course Indian fusion. Absolutely unforgettable. Second question - all of the DACs have RCA phono wired direct to the headphone contacts - they are all the same, wired from the same OPs.

Noted! I'm more likely to visit BKK than the UK, but I have added Asha's on my bucket list along with Gaggon. Although UK is #1 for Indian Food outside India, BKK is underrated. Maybe Top 3.

Beautiful, I don't have to worry about scaling. It will just be a natural process. I will never go back to just 6.3mm or 3.5mm for my CIEMs and stick with Chord DACs going forward. The RCA OUT is amazing headphone OUT option. Cheers for the design and implementation.