Saturday, 13 March 2021

HOW-TO: Partial Frequency Correction with Acourate. Spotify HiFi coming and a look at the evolution of music sales/formats from 1980-2020.

[See Addendum update as of Acourate 2.0.]

Over the years, I've discussed the use of DSP room correction in these pages (here and here for the more recent articles). In Acourate, there's no single-step macro to tell the software to limit the correction to certain frequencies as far as I can tell. Instead, I saw this comment by Dr. Uli Brueggemann in one of Mitch Barnett's early articles (2013) hinting at a way to modify the inversion step of the filter to accomplish that task. This post is a step-by-step procedure for those interested in doing just such a thing with the software.

Note that even though I'm showing the process here, I'm certainly not suggesting that it's necessary whatsoever. In my listening, a full-spectrum room correction sounds great with the frequency-dependent-windowing (FDW) algorithm Acourate uses. Over the years with friends and family who have had the time to sit and listen, I have never had anyone complain that my usual full-spectrum filter did not sound better than the uncorrected sound in my room (and on occasion, I have measured and applied DSP to my friends'/family's sound systems as well to similar effect).

It's always great to have options though!

Step 1: Prepare Acourate for the work directory, and use the LogSweep Recorder procedure to measure the impulse response of your room.

You can refer to the previous post here up to Item 6 (before the target curve creation).

For my room, the frequency response looks like this after running Macro 1 with my main speakers (Paradigm Signature S8) and subwoofers:

Step 2: Target curve creation.

Now we activate Macro 2 to draw out the target room curve. "Eyeball" your frequency response and create a curve with the idea of the frequencies you will be correcting in mind. Make sure the target curve's amplitude makes sense so that there's no massive discontinuity the moment the correction ends! Both the portion that will be corrected (primarily with peaks attenuated), and the uncorrected portion should be balanced in amplitude.

Here's what my target curve looks like:

Notice that I used the LowShelf function to create a +3dB accentuation to the frequencies below 100Hz, also LF and HF Roll-Off at the extremes. Feel free to enter a Subsonic filter frequency to remove extreme low-end stuff instead of the LF Roll-Off if you want even stronger suppression. I don't mind a bit of <20Hz rumble to feed the subs but getting rid of extreme lows can help with playback clarity. The Subsonic value you put in here will be carried forward into Macro 4 when the filter actually gets created.

Step 3: Calculate the gain level the filter produces.

To do this, we run a quick inversion (Macro 3):

And then run a Filter Generation (Macro 4) - the parameters don't matter much but I would keep the "Max. correction gain" at 0:

As you can see, the "Correction filter gain ratio approx.:" in this example is -1.5dB. Keep that number in mind.

Step 4: Create a flat "simple" 1:1 filter at the gain ratio amount... This flat "curve" will act as the portion of the frequency response which will not be corrected.

As you can see, I entered -1.5dB as per the result of Step 3. Then the program will tell you where this flat 1:1 filter has been saved to. In my example:

Step 5: Now load the 1:1 filter into curve bank number 6 from that "SimpleFilter" directory above:

Notice that I loaded the left 48kHz file ("Cor1L48.dbl") which is the native samplerate used in the LogSweep measurement.

Step 6: Now scope out potential points up to where you want the filter to affect; in this example, around 600-700Hz there appears to be some good crossover points we can naturally merge into the "Simple 1:1 Filter" uncorrected line:

Step 7: Now use the "Amplitude SplitNJoin" function to merge the correction inversion spectrum on the left (to even out the bass frequencies) with the flat uncorrected high frequency section to the right.

Using those crossover frequencies identified above (708Hz left, 669Hz right), I use these parameters in the "SplitNJoin" function for the left and right channels:

Left channel

Right channel

Notice that I'm putting the resulting hybrid curves back into the same inversion channel where currently "Pulse48Linv" and "Pulse48Rinv" resides. By the end of the "SplitNJoin" functions, you will see inversion curves that look like this for right and left channels:

Sometimes you might be off by a Hz here and there and the curves don't join naturally, instead you'll see a step up or down... You might need a little trial and error to get the crossover merge frequencies looking reasonably clean.

Step 8: Save Bank 4 as "Pulse48Linv.dbl" and Bank 5 as "Pulse48Rinv.dbl" in the work directory. The new merged curves now becomes the inversion correction curves used by the software to generate the FIR filter in the next step.

Step 9: Now create your filter with settings that work best for you. As usual, do a test convolution to check that the step response looks OK as well:

Here's one that worked for me (remember, if you set the Subsonic filter above in the target curve, you should see that same value in the Subsonic field):

Step 10: We can now double check that the filter is doing as it's supposed to... Pre- and Post-DSP filter frequency responses calculated with the test convolution:

Separated by 10dB for clarity.

Step 11: Load the new filter up and have a listen ;-). 

As usual, JRiver and Roon have worked well for me over the years with their convolution functions.

In Roon, I can easily switch between a few settings to listen to differences for myself including an even more "conservative" filter that only affects the bass up to 300Hz:

Hope this works out for you... :-)

Feel free to use REW to check frequency response with DSP on and off using the measurement microphone. One should have no difficulty confirming that indeed the DSP has affected the frequency response only within the selected range (ie. up to ~700Hz in this example). For example, here's a quick measurement I did with the filter above as a "proof of concept":

Overlaid 3 frequency responses aligned at 1kHz. Notice the "Partial" curve flattened out the bass and is similar to the "Full-Spectrum" curve in the lower frequencies. After 700Hz, it follows the "Uncorrected" curve. Left channel only.

Thanks to Uli for the general procedure and discussions with Mitch Barnett around some of the content here.

In Acourate 2.0 there has been an update to allow the user to set high frequency correction. This means it should be very simple now to perform the partial correction now! Excellent.


The big news in audio a couple weeks back was the announcement of a Spotify HiFi lossless service in the months ahead. It's about time! Finally with another of the "whales" (Amazon Music HD and now Spotify) in the lossless 16/44.1 club, Apple must be considering their future plans as well if they see significant consumer demand for the higher tier. I am mindful of the likelihood that high-bitrate lossy is good enough for the vast majority of music lovers. How many subscribers actually demand Spotify HiFi among its >140M worldwide subscribers will be interesting. However, even if just a few percent are interested, we're still looking at millions of subscribers!

Who knows at this point if Spotify will bother with "hi-res" content beyond 16/44.1. Personally it generally doesn't matter to me especially for streaming so long as they don't waste time and money with the MQA nonsense which they'll never get back ;-). The lack of any mention of hi-res suggests it won't.

I think Tidal HiFi especially is in a difficult spot at this point with a US$20/month price point and pseudo-hi-res MQA especially when Qobuz Studio is already down at US$15/month with true hi-res bitrate content on offer. With Spotify Premium lossy currently at $10/month (same price here in Canadian dollars), if they can target that $15/month spot with the HiFi tier if not even undercut that price, the name recognition and user interface quality I bet will win over many Tidal subscribers. This also will put some pressure on Roon I think given that it also runs on a subscription model (unless one were to buy the lifetime license) to expand integration if many subscribers use it for Tidal.

Personally, I cannot support Tidal for obvious reasons (I see it was recently bought by Square, Jack Dorsey of Twitter fame).

Qobuz, I'm guessing you guys will never show up here in Canada? I do hope Roon is able to do something with Spotify or Amazon HD given the limited options in a number of markets like Canada.

Also recently I saw this graphic of music sales from 1980 to 2020 (based on RIAA data if you want to see the details):

Check out that massive decline of CD sales numbers basically diminished now to about the same dollar amount as vinyl (vinyl is still more expensive so units of CDs sold still higher than LPs). Two decades of CD decline with about a decade-long vinyl "comeback". Yay...

The other interesting thing to be mindful of is that in total, the music industry has not recovered its peak sales from 1999. The 2020 number of a $12.2B industry in the US is ~54% of that peak just before Y2K! Remember this was all before "hi-res audio" was even a thing with DVD-A and SACD and of course as the Loudness Wars waged on and destroyed so much of our music quality with dynamic range compression among other processing in pop and rock genres primarily. I don't know about you folks, but personally even before turning 30 years old at Y2K, I was already struggling with maintaining interest in buying "new music" because of the poor sound quality.

Take care audiophiles - Spring ahead. Hope you're enjoying the music!


  1. 'Qobuz, I'm guessing you guys will never show up here in Canada?'

    Here in Australia, we're even more neglected by the music business (no HDTracks, prostudiomasters, etc) but I have just noticed qobuz has arrived!

    So, don't give up hope.


    1. Hi Ian. Where did you hear about qobuz in Australia? I signed up for a notification ages ago and haven't heard anything. The app is still geoblocked in the play store.

    2. On the qobuz web-site it asks if you want the Australian sub-site, which is:
      There are 3 plans available - studio premier monthly or annual and studio sublime.

    3. Thanks Ian, that's great news!

      Since the Canadian population is a larger than Australia, I guess there is hope in that our market will be similar if not a bit larger even...

      I hope Qobuz is listening. :-)

  2. Interesting. Now, if you could do the same but with Hypex Filter Design/ DLCP it would be much appreciated ;-) it would push forward a very slow burn project I have.

    If you were to overlay Napster use on that graph I think it might tell an interesting story.

    1. HFD eh? Interesting, will keep an eye out on that...

      The Napster story is interesting although I think the peak was back in 2000/2001 as far as I am aware. What is interesting is looking at the piracy trends, here's an interesting page with data to 2020:

      And here's a page with music piracy by age groups from 2017 data:

      These days, one could almost listen to anything off YouTube!

  3. Ok, you go me:
    “ Personally, I cannot support Tidal for obvious reasons (I see it was recently bought by Square, Jack Dorsey of Twitter fame....).”

    Could you elaborate? I must be missing something.

    I’m Mac based and use Audirvana. They support streaming through Qobuz and Tidal. I wonder if they’ll support Spotify as well.

    1. Hi R Lalonde,
      I'm referring mainly to Tidal's support of MQA although there are other concerns with this company and its owners.

      It's a matter of principle in that I view MQA as a dishonest company targeting audiophiles and the audiophile media. With Tidal being really their only "enabler" these days, I therefore cannot give money to them.

  4. Hoping that Spotify will be more open to third parties incorporating Spotify into third party players than Pandora and Amazon have been. I use Roon as my primary playback software for in-home because of how well they integrate my local library with Qobuz and Tidal. I dropped my Pandora premium subscription because it isn't integrated into Roon. Will add Spotify, Amazon, or Apple if they allow Roon to integrate them.

    1. I wouldn't count on Spotify being integrated into other players any time soon. I was a huge Spotify fan for 6 years. Used it as an integrated plugin on my Squeezebox Touch. The interface was great, as was the music selection. Then Spotify stopped supporting the access method that the Squeezebox plugin used. Squeezebox could not run the Spotify Connect app so that wasn't an option. One of the user-community support people patched together a plugin that tapped into the Spotify web interface, but it did not support all features and had limitations that made it unsuitable for my needs.
      I then purchased a Bluesound Node 2, which had a fully integrated Spotify app that tapped into all the important functionality. That was great for a year or so. Then Spotify discontinued support for any interface except Spotify Connect. Bluesound was able to install Connect on the Node 2, but it runs as a separate app. I then needed to bounce back and forth between 2 interfaces to access my local and internet music.
      At that point I dropped Spotify and switched to Tidal, which still has a plugin that runs in the BluOS interface.So, I don't see Spotify creating another non-Connect portal into their system. Spotify's goal is to present the same interface across all platforms and to keep your music playing as you move from device to device. Connect is their answer to that. The best you can hope for with other players is a trigger in the native app that bounces you out to the standalone Spotify Connect app. That is what Bluesound does. With a setup like this, Roon could not perform its cataloging and metadata magic on your Spotify library.
      I truly hope I am wrong about this, but I figure those of us with a local music collection are a small minority in the Spotify user base - and Roon users account for a small minority of us. Most Spotify subscribers are totally happy with Connect. 

    2. Hi Doug and Mark,
      Yeah, looks like this is going to be highly unlikely that Roon and Spotify could come together. Nonetheless, I do hope Roon can surprise us.

  5. I'm always amazed at how popular cassettes actually were for quite a while!
    No doubt spurred by the Walkman (and being able to be selective about which music you put on a tape).

    A similar, though not as massive, trajectory was had with digital downloads (and mp3 players) for essentially the same reasons. A hit in sound quality for convenience. I still shudder when thinking about the early digital download days where everyone put up with such crappy compression rates.
    We audio-heads were afraid a whole generation was being conditioned to accept poor sound quality but it seems those fears weren't totally valid.
    There seems to be quite a lot of people who still want good sound quality, not only seen in the buzzing of audio forums with lots of people newly getting in to better sound (especially maybe headphone oriented stuff), but also the fact the streaming services are recognizing the market for better sound quality (putting aside caveats on that claim).

    1. Hi Vaal,
      Yeah, cassettes had a pretty good 20 year run there. I think car audio was also another area that helped increase tape popularity like Walkmans. Mixtapes were certainly a great way to exercise some creativity!

      I totally agree, sound quality will always be desirable and young people are not deaf! (Even if the generations might not see eye-to-eye on what "good" music vs. "noise" sound like. :-)

      IMO there was never any fear that high-fidelity would not be desirable!

      For me, poor mastering beginning in the late-90's was more of an issue damaging sound quality than lossy compression ever was. Back around the late 90's into early 2000's, I remember download many poorly compressed MP3s with at best 160kbps done with some of the early encoders due to storage limitations. Back then with even poor computer speakers, I could easily tell the loss in quality.

      By about 2004-2005, with more storage and ripping to CBR 320kbps or high-quality VBR using LAME MP3 encoder, the sound quality was already excellent.

      As an audiophile, I think we should certainly aim for lossless streaming since the technology is capable these days. I just don't think there's any need to be be dramatic about modern high-bitrate MP3 or AAC sounding "terrible" or using those kinds of extreme adjectives.

  6. AT 73 I still own much music and continue to buy more CDs and a few lps when affordable. There was a great article in Stereophile about Reservoir Records and so I bought 2 to give it a try. At $10 it was a affordable gamble. Well, I now own 7 of Pete Malinverni's piano discs and one of Nick Brignola on Sax. You are not streaming this quality. The Malinverni discs are the best sounding piano recordings I own and he is a superb pianist. Not to be missed. Shipping is fast as well by Dr. Feldman who owns the label.

    I feel for the artists in all of this as their income from streaming is sorry. The artists that I am truly fans of; Diane Krall, Michael Buble', Alice Sara Ott, Helene Grimaud, Lang Lang, and others, I will buy their CDs to support them.

    What I am getting more concerned about is the USPS and their tardy deliveries. So from now on it will only be Amazon purchases. USPS tracking is nearly worthless as I am now into two weeks of waiting for a disc from Colorado and USPS can't even tell me where it is.

    Arch, you are right about the headphone listening as I would say I am at about 70% on cans with my Beyer DT 770 pro 250 ohm version (sealed) through a Schiit headphone amp; and my newest the ATH-700X that are a steal at $119 for an open back headphone through my Yamaha/Steinberg UR-22 USB box. Night stand listening in bed are the AT 50X's through a PreSonus headphone amp.

    1. Cool Jim,

      I have the "first gen" ATH-AD700 and AT-M50 headphones here and will use them with a number of different devices also. The AD700 was one of my first pair of open headphones and a pleasant surprise how open they sound even today! (They have some limitations of course - weaker low bass, somewhat peaky highs. I think your 700X probably improved the mids a bit.)

  7. Great writeup!

    DSP with Mitch

    1. Nice interview Jason,
      I've been to Mitch's place and he's definitely got a great set-up over on the Sunshine Coast.

      Keep up the great work on the videos!

  8. Hi Archimago,
    Two things come to mind about the drop in music revenue, the rise of gaming consoles and the rise of piracy, during the timeline.
    As for Hi Res, it really hasn't caught the imagination of the wider public, because they can hear perfectly good sound cheaper. I am not talking about quality in that statement as it appears to me from the small number of people I know, the actual interest in sound quality above MP3 isn't there.
    Do they appreciate the quality when I demo it, yes, do they want the associated price tag, no. shame. But if there is no desire for higher quality in audio, then you have to make it affordable to them. Streaming subscriptions aren't wildly priced, but the lower tier options do what those customers want.
    Hi Res will not go main stream as the recordings aren't in Hi Res, so what little there is as a difference wont be heard anyway, as most Hi Res is upsampled. plus the cost is higher, and the wider audience don't perceive any value to the extra cost.
    I still buy Hi Res versions when I can, simply because they are likely to have been well mastered, plus the bands I listen to are interested in the quality of their recording. Dua Lipa is likely to have heavy compression A winged victory for the sullen are likely to use the full dynamics and capture them, whether the format delivers higher than CD quality or not.
    It is good that CD quality is now streaming more widely, as many have said, beyond that and good mastering, it gets really niche.
    Long live great music and great mastering

    1. Hey Gordon,
      Yes, great point about video games and piracy (touched on above). We certainly have more entertainment options whether video streaming or interactive gaming content these days. I could not have imagined playing the kinds of games my kids have access to these days! And in turn, I don't think they've spent any money on music albums other than downloading singles off iTunes.

      Excellent comment about "hi-res"... Or basically "What hi-res?" in that there are barely any true hi-res albums out there once we weed out old analogue recordings, upsampled stuff, or stuff that could never benefit (like Dua Lipa).

      I'll still buy the rare hi-res acoustic/classical album. I was thinking back to my last hi-res purchase and it was last summer with the Reference Recordings of Tchaikovsky/Leshnoff.

      Needless to say, very few hi-res interests me these days. Lossless CD-resolution 16/44.1 of well-mastered content is all I would care about for streaming. I'll happily just buy the few true hi-res albums that might interest me.

  9. I don't stream at all, since I already have more than enough music to last me a lifetime. However I still buy new music all the time, both LP's and CD's. I have also stepped back from being interested in all things hi-res, because I have reached a point of playback where the quality of good recordings/mixes/pressings is very high. So high that only the very best hi-res albums are a real improvement, and IMO there are not too many hi-res albums that are truly better sounding. With LP's, things are a bit different. Buying 180g albums have proven to be worthwhile for me, so I like those a lot.

    So aside from debating the importance of the job of the sound engineers, I find that good LP's and CD's sound so amazing that I no longer bother with "audiohile" resolution except for the 180g LP's.

    My system is very revealing, very detailed and transparent, but also very natural sounding. It seems I've been lucky in putting together a system that will satisfy my hunger for music I love, and of a more than sufficient quality. My journey has not yet ended, but I could easily live with this for the rest of my life.

  10. There is absolutely nothing wrong with Darko's "All you need is". It has nothing to do with audio, but everything with psychology and perception. Unless that's not clear to the listener, the listener is the idiot.

  11. I find myself wondering why Apple doesn't switch to 48kHz instead of 44.kHz as their sampling rate. To be clear, I don't think the sample rate conversion is audible and I don't think 44.1 is problematic; but since almost everything is captured at 48k (or 96k), I wonder why the legacy of 44.1 lingers on. They could save an encoding step if they skipped the SRC, do a little marketing hand-wave, have a nice, pleasing round number as their sampling rate, with minimal impact on the bit budget. Is there something about downstream hardware expecting 44.1 that makes this hard to do?

    Related: I am unclear on if Mastered for iTunes files have been dithered to 16 bits, or if they are encoded as 44.1/24-bit AAC files. Hopefully someone on this blog can enlighten me.

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  13. Hello Archi. There is a much simpler way to partially correct frequency response. Acourate only corrects frequencies above the target curve. It ignores anything below the target curve. In my system (an 8 way active system), if I want Acourate to leave my midrange and tweeter unmolested, I do this:

    1. Take a sweep to confirm that all the drivers are at roughly the same level. Adjust the volume on the DAC or amplifiers and keep repeating sweeps until they are volume matched with all the other drivers. Delete this sweep, but note what gain you have applied to each channel.

    2. TURN OFF the amps to the midrange and tweeters. Repeat the sweep. The mid/tweets will now be way below the subs/woofers in level. Apply your target curve. Because the mids/tweets are way below the target curve, Acourate will ignore it and apply no correction.

    3. Turn them back on again and do another sweep of the full range to confirm that your mids/tweets are perfectly integrated.