[Argo Duck]

^ Indeed. Most scientists IME quickly learn humility from conducting experiments, me most definitely included

 

[evillamer]

Finally found a technical video that shows Sigma Delta has issues with tracking fast changing(very steep sloping) signals: It is called Slope Overload Distortion. Also Sigma Delta has Granular Noise distortion.
 
https://en.wikibooks.org/wiki/Analog_and_Digital_Conversion/Delta_Modulation
 

 
 

Slope Overload

 
 If the input signal is rising or falling with a slope larger than Δ/T, where T is the sampling time, we say that the sampler is suffering from Slope Overload. In essence, this means that in a Delta Modulation scheme, we can never have slopes larger than a certain upper limit, and functions that rise or fall at a faster rate, are going to be severely distorted. If the slope of m(n Ts)is greater then the slope of m(n Ts- Ts), then Slope Overload distortion occurs.

 
 

[size=20.007px]Granular Noise[/size] A problem with delta modulation is that the output signal must always either increase by a step, or decrease by a step, and cannot stay at a single value. This means that if the input signal is level, the output signal could potentially be oscillatory. That is, the output signal would appear to be a wave, because it would go up and down regularly. This phenomena is called Granular Noise.

When used in ADCs (Analog to Digital Converters), this problem can be solved by internally adding additional bit(s) of resolution that correspond to the value of Δ. This way, the LSBs (Least significant bits) that were added can be ignored in the final conversion result.

 
Watch From 28m:50seconds onwards:
 
 
 

 

[Sapientiam]

Slope overload is an issue for delta modulation - have you confused that with sigma-delta?

 

[skeptic]

  perhaps not too far afield - feedback theory is central to the internals of Delta Sigma converters and of course the analog buffers, I/V converters and filters after (almost) any DAC will employ feedback in some form or another
 

Spoiler: <Snip>

virtually all useful active circuits use negative feedback - the audiophile marketing "no feedback" really at best means no Global loop feedback and ignores local degeneration that feedback relations are needed to describe fully
 
but it is too big a subject to do justice to in any depth here
 
I did find the Pass audio distortion and feedback article unfortunate - I did press him over on diyAudio and he did admit my points of criticism - I consider his "exaggerating for effect" as pandering to the expected biases of the audiophile magazine audience
 
the "trick" for correct analysis that Pass skated past is that the signal level decreases by the gain of the intermediate stages as you follow the signal backwards from output to the input of a high loop gain global feedback amp
the reduced signal levels hugely reduces the distortion generation in each stage - at the input even undegenerated bjt diff pairs can add less than -120 dB distortion to the difference signal under ordinary operating conditions
 
there is no "tsunami" of IMD products in well designed high feedback amps operating within their limits - until you clip or try to "correct" a deadband
 
I do link, recommend just about everything else Pass has published
 

 
Putzeys feedback paper is a much more reliable popularization for audio enthusiasts with some EE knowledge - still not enough to learn the subject from http://linearaudionet.solide-ict.nl/sites/linearaudio.net/files/volume1bp.pdf (only a little bit of Laplace transfer function math...)

 
Thanks so much for the detailed response and explanation!  Tied up with a bunch of family stuff this weekend but looking forward to carefully reading the Putzey article as soon as time permits.  

 

[evillamer]

 
Quote:
 

  Slope overload is an issue for delta modulation - have you confused that with sigma-delta?

Correct me if I am wrong. Sigma Delta is an improvement over Delta Modulation by adding oversampling and noise shaping and filtering into the chain? As in Sigma Delta still employs some form of delta modulation(comparator) but at a much higher sampling rate? But the question I don't know is if the slope overload is still an issue with sigma delta or not?(you need 20x oversampling as per this pdf)
 
http://www.analog.com/media/en/training-seminars/tutorials/MT-022.pdf
Quote:

 Tests have shown that in order to obtain the same quality as classical PCM, delta modulation requires very high sampling rates, typically 20× the highest frequency of interest, as opposed to Nyquist rate of 2×. 

 

 HISTORICAL PERSPECTIVE
 
The Σ-Δ ADC architecture had its origins in the early development phases of pulse code modulation (PCM) systems—specifically, those related to transmission techniques called delta modulation and differential PCM. (An excellent discussion of both the history and concepts of the Σ-Δ ADC can be found by Max Hauser in Reference 1).
 
Delta modulation was first invented at the ITT Laboratories in France by E. M. Deloraine, S. Van Mierlo, and B. Derjavitch in 1946 (References 2, 3). The principle was "rediscovered" several years later at the Phillips Laboratories in Holland, whose engineers published the first extensive studies both of the single-bit and multi-bit concepts in 1952 and 1953 (References 4, 5).
 
In 1950, C. C. Cutler of Bell Telephone Labs in the U.S. filed an important patent on differential PCM which covered the same essential concepts (Reference 6). The driving force behind delta modulation and differential PCM was to achieve higher transmission efficiency by transmitting the changes (delta) in value between consecutive samples rather than the actual samples themselves. In delta modulation, the analog signal is quantized by a one-bit ADC (a comparator) as shown in Figure 1A.
 
The comparator output is converted back to an analog signal with a 1-bit DAC, and subtracted from the input after passing through an integrator. The shape of the analog signal is transmitted as follows: a "1" indicates that a positive excursion has occurred since the last sample, and a "0" indicates that a negative excursion has occurred since the last sample. 

 
 
 
Another interesting PDF:
 
 
http://www.numerix-dsp.com/appsnotes/APR8-sigma-delta.pdf
 

Section 5, page 1
 The work on sigma-delta modulation was developed as an extension to the well established delta modulation 

 

Section 6, page 2

 The name Sigma-Delta modulator comes from putting the integrator (sigma) in front of the delta modulator. Sometimes, the Σ−∆ modulator is referred to as an interpolative coder [14]. The quantization noise characteristic (noise performance) of such a coder is frequency dependent in contrast to delta modulation.

 

 
 
 

Section 7:
 
Three basic tasks are performed in the digital filter sections:
 
1. Remove shaped quantization noise: The Σ−∆ modulator is designed to suppress quantization noise in the baseband. Thus, most of the quantization noise is at frequencies above the baseband. The main objective of the digital filter is to remove this out-of-band quantization noise. This leaves a small amount of baseband quantization noise and the band-limited input signal component. Reducing the baseband quantization noise is equivalent to increasing the effective resolution of the digital output.
 
2. Decimation (sample rate reduction): The output of the Σ−∆ modulator is at a very high sampling rate. This is a fundamental characteristic of Σ−∆ modulators because they use the high frequency portion of the spectrum to place the bulk of the quantization noise. After the high frequency quantization noise is filtered out, it is possible to reduce the sampling rate. It is desirable to bring the sampling rate down to the Nyquist rate which minimizes the amount of information for subsequent transmission, storage, or digital signal processing.
 
3. Anti-aliasing: In practice, the input signals are seldom completely band-limited. Since the modulator is sampling at a rate much higher than the output Nyquist rate, the analog antialiasing filter before the modulator can roll off gradually. When the digital processor reduces the sampling rate down to the Nyquist rate, it needs to provide the necessary additional aliasing rejection for the input signal as opposed to the internally generated quantization noise.
 
There are a number of factors that make it difficult to implement the digital decimation filter. The input sampling rate of the modulator is very high and the MOTOROLA 7-3 digital decimation filter must perform computationally intensive signal processing algorithms in real time. Furthermore, higher order modulators produce highly shaped noise as indicated in the spectrum shown in Figure 6-7 and Figure 6-8. Thus, the decimation filter must perform very well to remove the excess quantization noise. Applications like high quality audio conversion impose the additional constraint that the digital signal processing must perform its task without distorting the magnitude and phase characteristics of the input signal in the baseband. The goal is to implement the digital filter in a minimum amount of logic and make it feasible for monolithic implementation. 

 

[mikoss]

Sonic Defender did you ever have that meet in Ottawa to do the testing? I heard the Yggy again today and was impressed with the detailed presentation. Just wondering the results when you do have the meet.

 

[Sonic Defender]

Sonic Defender did you ever have that meet in Ottawa to do the testing? I heard the Yggy again today and was impressed with the detailed presentation. Just wondering the results when you do have the meet.

Sadly we are seriously considering putting the meet off until late September as it seems summer is a tough time to compete with. For those that don't live in a true winter-bound climate, it may be hard to understand that when a brief summer hits us, people try to cram so much stuff into such a short period of time that something has to give (like headphone meets).
 
I don't mind as waiting will allow us to have more time to prepare as well as get enough subjects. Long way of saying, not yet.

 

[mikoss]

Cool well maybe I can make it to Ottawa in sept. Enjoy the summer either way...

 

[rkt31]

I'm simply surmising. I have not actually heard any mult-bit beef-roast nor do I know much about it really other than what little Jason / Moffat have said. However, it would appear that you may know more than me about this multi-bit beef-roast! Please tell me more! Many inquiring minds want to know! Maybe we can ask Darko?

Yeah, I know. TT is more for my spoiled rich cousins and nephews in Taiwan who don't have to do anything.

TT has better headphone amp than Hugo hence expensive. 2qute has no amp like yggy. what more it is cheaper than yggy.

 

[bmichels]

TT has better headphone amp than Hugo hence expensive. 2qute has no amp like yggy. what more it is cheaper than yggy.

 
did you really hear a difference between booth AMPs ?  With several headphones, I compared my HUGO with a TT and couldn't head a significant difference ? 

 

[dan.gheorghe]

I've managed to get my hands on an old theta dspro basic. I know it's not in the same league with gen V, but I was still astonished by its performance. Incredible performance from a dac designed ~25 years ago.

 

[evillamer]

  I've managed to get my hands on an old theta dspro basic. I know it's not in the same league with gen V, but I was still astonished by its performance. Incredible performance from a dac designed ~25 years ago.

 
Excellent Review(as always). Can't wait for you to review on the Theta DS Pro or even the Schitt Yggdrasil.
 
 

Wood sounds like wood, metal sounds like metal, etc.

 

 Exploding attack and laser decays, leading to a fast, energetic & exploding sound signature. I find this DAC to be quite unique in this department.

 

This was another dac that proved to me why I should be a R2R fan. I just loved the textures, voices and natural tonality this DAC was capable of. Most of the delta sigma DACs today tend to have a digital sound, unnatural and harsh.

 

[evillamer]

Some have the misconception that Modern DACs by merit of being newer(due technological advancements) sound better.(think windows 95 vs modern windows 8.1). However it seems that this is not the case with audio hardware. It's the design and quality of the components used that matters more than the age of the product.

 

[Sonic Defender]

  Some have the misconception that Modern DACs by merit of being newer(due technological advancements) sound better.(think windows 95 vs modern windows 8.1). However it seems that this is not the case with audio hardware. It's the design and quality of the components used that matters more than the age of the product.

While I'm sure this might be true, it isn't safe to assume that this is true frequently. Technological advances are very important and the notion that older always used better quality I'm not sure if that is accurate either. You might have some of the most expensive capacitors from the 90s that were extremely expensive simply due to scale of economy, newness of the technology, or any other number of reasons. Perhaps today even very affordable capacitors are equally as reliable and have better specs. While it is nice to assume older was always better, not likely. People always needed to make margin and corners were cut then as they are now when design parameters allow for it.
 
Just the other day somebody brought in some quite old Bang and Olufsen speakers and a very long all in one amp, turntable and cassette deck. I threw them all in the recycling bin at work as they were old enough that even entry level Polk speakers would sound better without a doubt. 

 

[evillamer]

I am not saying that older products used high quality or expensive components by default. I am saying that quality of the components used and the design of the product outweights the age of the product.

e.g. A 2015 newly designed dac doesn't necessary automagically means it is better than a 2010 dac.