# [music-dsp] prime number's role in reverb

Jens Blomquist metal.aero at telia.com
Fri Jul 11 00:58:57 EDT 2003

```Well, I'm no expert but I've implemented a couple of reverbs.

May I ask you a couple of questions?

1. You name the modulation speed, but what about the amount?
2. Same modulation for all delay lines?
3. How does the feedback matrix look like?

The choise for prime numbers should be pretty obvious in theory.
Look at the third set: 1000*3 = 1500*2.

In practice? I don't know. The best sounding reverbs I have
created is far from realistic. I usually go crazy with the
modulation as I like the "unrealistic" thick density better
than the dull and often metallic sounding reverbs out there.

Also, things get rather complicated when using modulation. Maby
someone here can tell us what difference prime numbers will
make in such a case?

br
Jens

----- Original Message -----
From: <y.shi at gpe-hkg.com>
To: <music-dsp at aulos.calarts.edu>
Sent: Thursday, July 10, 2003 11:39 AM
Subject: [music-dsp] prime number's role in reverb

>
> Dear list:
> I have improve the ring noise by modulating the delay line. Sorry to bore
> you.
> Yet i have another question about prime number:
> Most article mentioned that the delay length of FDN reverb must be prime
> number,for example,919,1129,etc.
> Today,i expermented on three sets of delay line,as below:
> The first delay sets is pure prime number:
> m=[919 997 1061 1093 1129 1151 1171 1187 1213 1237 1259 1283 1303 1319
1327
> 1361]
> The second sets is not prime number,but similar to set 1:
> m=[900  990  1060 1090 1120 1150 1170 1180 1210  1230 1250 1280 1300 1310
> 1320 1360]
> The third sets is definitly regular even number:
> m=[900 950  1000 1050 1100 1150 1200 1250 1300  1350 1400 1450 1500 1550
> 1600 1650]
> I implement them in Csound, each delay line is modulated by LFO slightly
> (0.1Hz).The dry source included drum and a piece of classic guitar solo.
> All processed result are saved to separated wave files.The monitor device
> is a Mona Echo 2496 soundcard and Event 20/20 loudspeaker.
> To my surprise,I indeed could not find any difference from the three
> sets,as well as  the spectrum and decay feature (observed in Cooledit
Pro's
> Frequency Analysis window).Each wave sounds just the same to me!
> But, why? The prime number have what role in reverb?
>
> Thanks and Best Begards!
>
> +---------------------------------------------+
> |  Shi-Yong  (Ê¦ÓÂ)                           |
> |  R&D,GPE Limited,Shenzhen,China             |
> |  Tel: (86 755) 8246 3828 ext. 380           |
> |  Fax: (86 755) 8246 0140                    |
> |  mail to:  y.shi at gpe-hkg.com                |
> +---------------------------------------------+
>
>
>
>
>
>                     y.shi at gpe-hkg.com
>                     Sent by:                      To:
music-dsp at aulos.calarts.edu
>                     alarts.edu                    Subject:     [music-dsp]
"ring" tail in FDN reverb
>
>
>                     03-07-08 17:20
>                     music-dsp
>

>
>
>
>
>
>
> Dear list:
>        I'm tring a 32 delay lines FDN algorithm in Csound just now.The
> processing speed is very slow on my P4,and the sound quality is not much
> better than 16 delay lines.A metallic "ring" noise about 2.5kHz can be
> heard in the reverb tail in some audio sample (guitar solo).
>        I don't know why.The delay line I used is below:
> m=[1693 1723 1747 1777 1801 1823 1847 1873 1901 1931 1951 1979 2003 2029
> 2053 2081 2111 2137 2153 2179 2203 2237 2267 2293 2311 2339 2357 2381 2411
> 2437 2459 2503]
>        Should I try more different sets of delay line length again and
> again? Any suggestion?
>        Thanks!
>
> Best Regards!
>
> +---------------------------------------------+
> |  Shi-Yong  (Ê¦ÓÂ)                           |
> |  R&D,GPE Limited,Shenzhen,China             |
> |  Tel: (86 755) 8246 3828 ext. 380           |
> |  Fax: (86 755) 8246 0140                    |
> |  mail to:  y.shi at gpe-hkg.com                |
> +---------------------------------------------+
>
>
>
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>
>
>
>
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FAQ, source code archive, list archive, book reviews, dsp links
http://shoko.calarts.edu/musicdsp/
> http://ceait.calarts.edu/mailman/listinfo/music-dsp

```