Real World Dynamic Range

Hi Dafydd,

Most of my experience of late is in automotive audio - radio head units, external amplifiers, blue tooth hands free kits, etc.  Previously I was also involved in PC audio design, set top boxes, & home theaters.  In my experiences, most of these types of systems require DR (assuming DAC) in the 96dB - 105dB range, depending on the audio content.  Other "limiting" factors in the design take into account the gain & noise associated with any external op-amps or audio power amps.  Sometimes our customers don't understand the limitations in their systems and they go with the same legacy requirements of 100dB, or whatever they've used in the past, without really looking at all pieces of the signal path.  So in a sense, this is a very good question - what do our customers use today and what do they really need based on all their other signal chain blocks?

Here are typical system requirements for automotive, defined as measured SNR or DR from audio source to speaker load:

Radio head units, external amps, and BT modules: DR 85-100dB, depending on level of system; audio DAC's typically spec'ed in the 100 - 105dB range, audio ADC's anywhere from 90-105dB, depending on system.

The DAC's are typically in the 100-105dB range and fairly consistent. Even in a Blue Tooth module, 100dB or more is used because of audio content being supported (higher quality than voice).  Audio ADC's specs vary more, with 105dB in the highest performance external amps. The ADC's vary a lot because of different types of audio inputs, each having their own unique SNR/DR specs (CD, DVD, digital radio, satellite radio module, etc).

I do feel the THD+N spec is becoming more important.  More customers ask about this now than they ever have.  DR and SNR are still critical, but adding more detail about THD+N in the datasheets is a great idea.

- Todd

Hey Dafydd,

I am in perhaps a different boat of what is called "Mastering engineering" where I am designing mastering gear/equipment.  Mastering, as you may know, happens after the recording studio but before the manufacturing phase of an artist's album (every piece of music on everyone's MP3 player has probably been mastered if it is a commercially released set of music).  Look in any commercially released CD's liner notes and one will see that it was recorded and mixed in the recording studio by someone or a group of people, then mastered by someone else (usually).  Mastering is typically NOT done in a recording studio environment due to acoustic comb filtering coming off of large consoles (in fact, the less "stuff" you have in front of you, the better).  Thus if the art of mastering is "taking the bugs out of the music," then the art of recording in the studio must be the art of "putting the bugs into the music" :-)

Also to note, most times, "that slamin' hit record sound" comes from mastering, although captured in the recording studio, it isn't until mastering that it is finessed and brought forth with various "black art" tricks in the mastering engineer's secret weapons arsenal including various types of distortion (which is a relatively new approach compared to the original mastering intent from, say, the 1950s "Transfer Engineering").  There's good distortion and bad distortion for a particular genre of music.  Because an album is usually recorded and mixed over a long period of time, differences in spectral content (EQ) and energy (RMS over frequency) occur and is why mastering is important.  Mastering will fix these variances, and place all the proper digital codes on the CD for manufacturing and also space the songs of an album properly for an overall album sound (makes it sound like an album rather that a collection of songs).

In mastering, we are concerned with keeping the best dynamic range because of mastering for multiple formats (and not "tainting" the music with limitations in our equipment), whether it be DVD Audio, red book for CD or for MP3.  For our archive and analog / digital processing in mastering more bits and dynamic range is better, for example, for the future with the proverbial Limp Bizkit reunion tour 20 years from now including classic tracks, remastered...Whatever a Limp Bizkit is... I dunno...

Ideally 144dB would be grand ;-)  or see also: http://www.lavryengineering.com/index_html.html for a "127dB" ADC...  Yes, for mastering, we sometimes "jack" out into the real world and use analog equipment (vacuum tube or otherwise) in addition to digital equipment in a rack or digital audio workstation.  Techniques like parallel compression, mult-band compression, DSP for noise removal, dynamic EQ (digital or analog) and even special distortion are used.

However, with all the possible specsmanship, at the end of the day, sometimes a really "good" converter may be too good and reveal all sorts of "digititis" of which the best vacuum tube gear we have does not sufficiently smooth over the harsh sounding signal (perhaps older 1990s vintage 16-bit ADAT recordings).  Some of us mastering folk have secret weapons to deal with these things somtimes...

I will admit that mastering engineering is a niche if I were a TI chip sales person, but I will say that there are throngs of students (okay, maybe not throngs) studying the oft unknown art mastering and thusly the specialized equipment needs thereof.

I should note that mastering is not exactly like audiophilery or audiophoolery, but it can approach it... we don't use rooms filled with argon except on alternate thursdays...

Cheers,

-chris

Independent Electrical Engineer / Software Engineer / RF Engineer / Mastering Engineer

Hello Chris,

Awsome post, I appreciate your feedback. The image of mastering studio's is exactly what you described - usually have minimal equipment in the room, maybe some high end EQ and compression to tune each song, so that they give one overall finished "feel" to an album.

Even with the best chips on the market, a lot of this equipments "sound" does come down to a design engineers skills and understanding of the effect of one part, on another. Dan Lavry's products are very much respected in the market, and his knowledge of clocking and jitter really are second to none. 

Jitter, Layout, Impedance matching, low noise power supplies and matching the right signal chain components to the right signal levels (of noise and distortion) are the things that separate the men from the boys.

By the way - I'd be very interested to know what products your designing, feel free to PM me with details.

Cheers,

/Dafydd

Cool... Glad I could help...  The PM feature seems to be turned off in the forums here.....

Harrumph....

-chris

Hi Chris,

The PM feature isn't turned off, it's just set-up REALLY stupidly (is that a word?).  What you have to do is friend someone and then you will see that you can "start a conversation with them."  You can also go in to your profile and set it up so that anyone can start a conversation with you.  We are working right now to change the default from "only friends can start a conversation" to "everyone can start a conversation."  I hope this helps for now.

Thanks!

Nancy

Thanks Nancy... I was beginning to wonder why "I had no friends" on the forum here... :-)

Cheers

Hi Dafydd - long time no speak, I hope that everything is good with you !

To answer your question - as much as possible, however we have to be mindful of both cost and implementation complexity because we will normally be looking for more than a stereo pair of channels ...

For our application at the end of the chain in large scale PA pro-audio 107dB (flat) or 110dBA (analog in to analog out) would be the minimum that is OK. This is not so much because that drange is actually required but because customers often use the equipment in combination with other gear and almost always do not optimise the gain structure to minimise the system noise floor (sometimes though ignorance, often for good reasons). Therefore the more drange we have the lower the noise floor and this is important with the very sensitive arrays of horn loaded speakers that are used. 

Ideally we would want getting better than 115dB (flat) again analog in to analog out. Much more than that and we will be getting in to a desire to print a better 'spec than actually make much difference to our customers performance.

Ben